Step 1

Melt the butter in a large skillet over medium-high heat. Add the onions and peppers and cook, stirring occasionally, until softened and starting to caramelize in some spots, 6 to 7 minutes. Add the garlic and cook, stirring, until fragrant, about 1 minute. Stir in the beef and cook, breaking up the meat with a wooden spoon or spatula, until it is browned, no longer pink in the middle and cooked through, 7 to 8 minutes.

Step 2

Stir in the tomato sauce, ketchup, brown sugar, Worcestershire sauce, mustard, red wine vinegar, paprika, cayenne pepper, 1 teaspoon salt and a generous amount of black pepper and simmer, stirring occasionally, until thickened and heated through, 5 to 6 minutes. Spoon the meat onto the toasted buns.