If you’d like to brine the pork chops, do so 45 minutes to 12 hours before you plan to start cooking (see recipe notes).
Pat the pork chops very dry on both sides with paper towels (discard the brine if using).
Place a rack in the center of your oven and preheat the oven to 350 degrees F. In a wide, shallow bowl (a pie dish works well), stir together the flour, cumin, paprika, 1/2 teaspoon salt, and 1/4 teaspoon pepper.
In a Dutch oven or similar large, deep, oven-safe pot with a tight-fitting lid, heat the oil over medium heat. Dredge the pork chops in the flour mixture on both sides, shaking off any excess. Reserve the remaining flour mixture.
Once the oil is hot and shimmering, gently lower the chops into the pan (lower them away from you to prevent splattering yourself with oil). Cook on both sides until brown and crisp, about 3 to 4 minutes per side (they will not be fully cooked through). If the pork chops will not all fit in your pan without touching, cook them in batches. Transfer to a plate.
Reduce the heat to medium low heat. Add the onions, remaining 1/2 teaspoon salt, and remaining 1/4 teaspoon pepper. Cook, stirring often, until the onions are completely softened, about 15 minutes. Stir in the Dijon mustard.
Sprinkle 3 tablespoons of the reserved flour mixture over the top of the onions. Stir to combine and cook for 2 full minutes, stirring often. No white bits of flour or lumps should remain
Slowly add 1 1/2 cups of the stock, stirring constantly. With a wooden spoon, scrape along the bottom of the pan to remove any brown bits. Let simmer until the sauce starts to form a cohesive mixture and is slightly thickened. Return the pork to the pot, nestling it in a single layer.
Cover the pot and place it in the oven. Bake the smothered pork chops until the pork is tender and reaches 135 to 140 degrees F on an instant read thermometer, about 30 to 40 minutes (pork is considered safe to eat at 145 degrees F, but its temperature will continue to rise as it rests).
Transfer the pork chops to a plate. Return the pot to the stovetop. Turn the heat to medium, add the remaining 2 1/2 cups stock, and reduce, stirring often and scraping along the bottom of the pan, until the sauce thickens into a gravy, about 15 minutes. Stir in the balsamic vinegar.
Remove from the heat. Return to the pork chops and any juices that have collected on the plate to the pan to let the gravy rewarm them. Serve hot, smothered with gravy, and garnish with chopped parsley or thyme.
*BRINE: If time allows, for the juiciest possible pork chops, submerge them in 4 cups water mixed with 3 tablespoons kosher salt for 45 minutes at room temperature (or up to 12 hours in the refrigerator). Drain and pat dry. Reduce the salt in the dredging mixture to 1/4 teaspoon and the salt added to the onions to 1/4 teaspoon.
TO STORE: Refrigerate pork chops in an airtight storage container for up to 3 days.
TO REHEAT: Gently rewarm leftovers in a baking dish in the oven at 350 degrees F or in the microwave.
TO FREEZE: Freeze pork chops in an airtight, freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.