Preheat your oven to 275°F (135°C). Remove the membrane from the back of the ribs by sliding a knife under it and pulling it off with a paper towel for better grip.
In a bowl, combine ¼ cup brown sugar, 1 tablespoon smoked paprika, 1 tablespoon black pepper, 1 tablespoon kosher salt, 1 tablespoon chili powder, 1 tablespoon garlic powder, 1 tablespoon onion powder, and 1 teaspoon cayenne pepper (optional). Mix well to create the spice rub.
Rub yellow mustard all over the ribs. This will help the spice rub adhere to the ribs and you won't be able to taste the mustard, so no worries. Generously coat both sides of the ribs with the spice rub, pressing it into the meat.
Wrap the ribs tightly in aluminum foil, ensuring no steam can escape. Place the wrapped ribs on a baking sheet and bake in the preheated oven for 3 1/2 hours, or until the ribs are tender.
While the ribs are baking, prepare the BBQ sauce. In a medium saucepan, combine 1 cup ketchup, ¼ cup dijon mustard, ¼ cup apple cider vinegar, ¼ cup brown sugar, 1 tablespoon Worcestershire sauce, 1 teaspoon smoked paprika, 1 teaspoon garlic powder, 1 teaspoon onion powder, ½ teaspoon black pepper, ½ teaspoon kosher salt, and ¼ teaspoon cayenne pepper (optional). Bring to a simmer over medium heat, stirring occasionally.
Reduce the heat to low and let the sauce simmer for 15-20 minutes, or until it has thickened to your desired consistency. Remove from heat and set aside.
After baking, remove the ribs from the oven and carefully unwrap them. Increase the oven temperature to 400°F (200°C).
Brush a generous amount of BBQ sauce on both sides of the ribs. Place the ribs back on the baking sheet (unwrapped) and return to the oven for 15-20 minutes. Repeat this process 2 or 3 times or until the bbq sauce is caramelized and slightly charred.
Remove the ribs from the oven and let them rest for a few minutes before slicing. Serve with additional BBQ sauce on the side. Enjoy!