How to Make It
Heat oven to 275° F. Make the rub: In a small bowl, combine the chili powder, coffee, cumin, 2 tablespoons of the brown sugar, ½ teaspoon of the cayenne, 2 teaspoons salt, and 1 teaspoon black pepper.
Place the ribs on a large rimmed baking sheet. Rub the ribs with the spice mixture and tightly cover the baking sheet with foil. Bake until tender and the meat easily pulls away from the bone, 2½ to 3 hours.
Meanwhile, make the sauce: In a saucepan, combine the ketchup, vinegar, molasses, tomato paste, the remaining 2 tablespoons of sugar and ¼ teaspoon of cayenne, and ½ teaspoon black pepper. Simmer, stirring occasionally, until slightly thickened, 8 to 10 minutes. Transfer ½ cup of the sauce into a small bowl for serving.
Heat grill to medium-high. Grill the ribs, basting with the remaining sauce and turning occasionally, until just beginning to char, 4 to 5 minutes. Serve with the reserved sauce.