Ingredients

• For the Cake:
• 3 cups cake flour
• 3/4 cup uncooked oatmeal
• 2 tsp. baking powder
• 1 tsp. baking soda
• 1/2 tsp. salt
• 1 cup unsalted butter, at room temperature
• 1 cup light brown sugar, firmly packed
• 1/2 cup granulated sugar
• 2 TBSP molasses
• 2 tsp. vanilla extract
• 3 large eggs
• 2 large egg yolks
• 1 cup plus 2 TBSP full fat buttermilk
• For the Filling: (not a huge fan, next time try SMBC)
• 1 cup shortening
• 1 cup powdered sugar
• 1 (7oz) jar marshmallow fluff
• 1 1/2 tsp. Vanilla extract
• For the Crumbles: (huge amount of crumbles!)
• 1 (17.5 oz) Oatmeal Cookie Mix (I used Betty Crocker)
• 1/2 cup unsalted butter, melted

Instructions

1. For the Cake:
2. Preheat oven to 350°F.
3. Grease and flour three 6 inch pans and set aside.
4. Sift together the flour, oatmeal, baking powder, baking soda, and salt set aside.
5. In the bowl of a stand mixer fitted with a paddle attachment, beat the butter on medium speed until smooth.
6. At the sugars and mix on medium high until the butter is light and fluffy, about three minutes.
7. Stop the mixer and scrape down the bowl.
8. The mixer to medium low and add the molasses, vanilla, and the eggs and egg yolks, one at a time until combined.
9. Stop mixer and scrape down the bowl.
10. Turn the mixer to low and add the flour mixture in three batches, alternating with the buttermilk, beginning and ending with the flour mixture.
11. Mix on medium for no more than 30 seconds after the last streaks of dry ingredients are combined.
12. Evenly divided the batter between the prepared pan.
13. Bake for 30 to 35 minutes or until a toothpick inserted into the center of the cakes comes out clean.
14. Let them cool on wire rack for 10 to 15 minutes before removing the cakes from their pans.
15. Keep the oven at 350F for the crumbles.
16. For the Crumbles:
17. Mix together the cookie mix and melted butter. 
18. Mix with your hands until crumbles form.
19. Spread out the mixture onto a baking pan lined with parchment paper.
20. Bake for 10 minutes. 
21. Then flip the crumbles with a spatula and bake another 5-10 minutes depending how crunchy you want your crumbles to be.
22. For the Filling: 
23. Cream the shortening, powdered sugar, and vanilla together until smooth.
24. Add the marshmallow fluff and mix until fully combined. 
25. Putting the cake together:
26. Place a cake layer on a cake pan. 
27. Take 1/3 of the filling and spread it on top of the layer.
28. Add 1/2 cup of crumbles.
29. Repeat until all the filling and cake layers are gone. 

Swiss Meringue Buttercream Recipe

 Prep Time 25 minutes  Cook Time 5 minutes  Total Time 30 minutes

Ingredients

• 5 large (150 grams) egg whites
• 1 1/4 cups (250 grams) granulated sugar
• 3 sticks (340 grams) unsalted butter, at room temperature
• 2 teaspoons pure vanilla extract
• 1/4 teaspoon fine salt

Directions

1. Wipe the bowl of an electric mixer with paper towel and lemon juice or vinegar to remove any trace of grease. Make a double boiler by placing the mixer bowl over a saucepan of simmering water, making sure the bowl doesn’t touch the water.
2. Add the egg whites and sugar to the bowl, whisking constantly but gently, until temperature reaches 140°F, or until the sugar has completely dissolved and the egg whites are hot.
3. Attach the bowl to the mixer fitted with the whisk attachment and begin to whip until the meringue is thick, glossy, and the bottom of the bowl no longer feels warm, about 7 to 10 minutes.
4. Switch over to paddle attachment and, with mixer on low speed, add the butter cubes, one at a time, until incorporated. Continue beating until it has reached a silky smooth texture. If the buttercream curdles simply keep mixing and it will come back to smooth. If the buttercream is too thin and runny, refrigerate for about 15 minutes before continuing mixing with paddle attachment until it comes together. Add the vanilla and salt, continuing to beat on low speed until well combined.
5. Add additional flavors, purees, or mix-ins as desired.

To make ahead:

1. Keep in airtight container in refrigerator for up to one week or in the freezer for up to 2 months. Let come to room temperature and rewhip in the mixer with the paddle attachment before using.

Recipe Notes

This makes enough frosting to generously frost a 9-inch two layer cake or about 2 dozen cupcakes. This recipe can easily be doubled.

Prep: 25 min Cook: 5 min Total 30 min Use for Oatmeal Cream Pie Cake

Ingredients

• 6 large egg whites (240g)
• 2 cups (400g) granulated sugar
• 1 and 1/2 cups (3 sticks; 350g) unsalted butter, softened but still cool and cut into Tbsp size pieces (*see note*)
• 2 teaspoons pure vanilla extract
• 1/8 teaspoon salt

Instructions

1. Separate the eggs: If you haven’t done so yet, separate the eggs first. Separate 1 egg white in a small bowl, then place the egg white in your heatproof mixing bowl. Repeat with the remaining egg whites. This way, if a yolk breaks in one of them, you don’t waste the whole batch.
2. Whisk sugar into the egg whites, then set the bowl over a saucepan filled with just two inches of simmering water over medium heat. Do not let the bottom of the egg whites bowl touch the water. Whisk the whites and sugar constantly until sugar is dissolved and mixture has thinned out, about 4 minutes. The mixture will be thick and tacky at first, then thin out and be frothy white on top. To test that it’s ready, you can use your finger or an instant read thermometer. Lightly and quickly dip your finger (it’s very hot, be careful) and rub the mixture between your thumb and finger. You shouldn’t feel any sugar granules. If using a thermometer, the temperature should read 160°F (71°C).
3. No need to let it cool down to start this next step– it’s important to begin mixing while it is still warm. Transfer mixture to the bowl of a stand mixer fitted with a whisk attachment (if you aren’t already using the metal bowl that comes with it). You can use a hand mixer instead, but this step takes awhile and your arm tires quickly. On medium-high speed, beat the mixture until stiff glossy peaks form and the meringue is no longer warm to the touch, at least 10-15 minutes. On particularly humid days, this has taken me up to 17-18 minutes. If it’s still not reaching stiff peaks, stop the mixer, place the bowl–uncovered–in the refrigerator for 10 minutes, then return to the mixer and continue beating until stiff peaks form. (This has always worked for me when it’s taking forever to reach stiff peaks.)
4. If the bowl and meringue still feel warm, wait until both cool to room temperature before adding the butter in the next step. Feel free to place it in the refrigerator. A warm bowl and meringue will melt the butter.
5. Switch the stand mixer to the paddle attachment. On medium-high speed, add the butter 1 Tablespoon at a time. Wait for the butter to fully mix in before adding the next Tablespoon. After all the butter has been added, turn the mixer down to medium speed and fully beat in the vanilla and salt, about 30 seconds.
6. Your Swiss meringue buttercream should be thick, creamy, and silky smooth and is ready to use on any cake, cupcake, or other confection.
7. Too Thick or Too Thin: If your meringue has separated, curdled, or is too thick at any point after you mix in all of the butter, place the mixture in your heat-proof bowl back over a pot of 2 inches of simmering water. Without stirring, let the edges of the meringue warm up and become liquid (the center of the meringue will still be solid), about 1-2 minutes. Remove from heat and return to the mixer. Beat meringue on low speed for 30 seconds, then switch to medium-high speed and beat until smooth, about 2 minutes. Works every time. If your mixture has become too thin and soupy after you add the butter, place the entire bowl in the refrigerator (covered or uncovered, doesn’t matter) for 20 minutes to cool down, then return it to the mixer and beat on medium-high speed until thickened. More troubleshooting tips in the post above.

Notes

1. Make-Ahead, Storing, & Freezing Instructions: Swiss meringue buttercream is great left covered at room temperature for 1-2 days, but after that, refrigerate it for up to 5 days or freeze up to 3 months. If freezing, store in an airtight container, then thaw it at room temperature on the counter. Once completely at room temperature, about 72°F (22°C), place into the bowl of your stand mixer fitted with a paddle attachment and beat for 2-3 minutes until creamy again. If it separates or curdles, see step 8.
2. Yield: This recipe yields about 5 cups of frosting, which is enough to fill and frost a two layer 9-inch cake with a generous amount, to fill and frost a three layer 9-inch cake with just enough frosting, to lightly frost 2 dozen cupcakes, to heavily frost 1 dozen cupcakes (I had just enough for the huge swirls on 12 of the pictured cupcakes), or a 9×13 inch sheet cake (with some frosting leftover).
3. Egg Whites: For best success, I recommend using fresh eggs instead of carton egg whites. Here are all my recipes using leftover egg yolks. Eggs separate much easier when they’re cold. Separate the egg whites one at a time and place the egg white into a large heat-proof mixing bowl (or a double boiler or the metal mixing bowl from your stand mixer) before separating the next. This way, if a yolk breaks in one of them, you don’t waste the whole batch.
4. There’s almost always a way to fix “ruined” Swiss Meringue Buttercream and it usually has to do with temperature. See step 8 as well as my troubleshooting tips in the post above.
5. Butter: This buttercream will thin out and become liquid-y if the butter is too warm. Make sure you’re using butter that is slightly cooler than proper room temperature butter. Remove butter from the refrigerator and set it out for just 30-40 minutes before you need to add it to the meringue. Sometimes meringue takes longer than usual or it needs a break (see Troubleshooting above) and in that case, you should place the butter back into the refrigerator for a few minutes so it doesn’t get too warm sitting out. The butter should be cool to the touch. For accuracy, I recommend using an instant read thermometer. Butter should be 60°F (16°C).
6. Flavors & Colors: For flavor ideas including chocolate, see my Can I add flavors? FAQ above. For coloring, it’s best to tint this frosting with gel food coloring so you aren’t adding a lot of extra liquid. Beat food coloring into the frosting on low speed after you add the vanilla extract and salt.
7. Half or Larger Batch: You can halve this recipe. The egg white/sugar mixture won’t take as long to cook and the meringue won’t take as long to reach stiff peaks. I do not recommend making larger batches at a time because it will quickly overcrowd and wear out your mixer. If you need more batches, make them all separately.