Hard Cider Brats and Peppers

Name: Hard Cider Brats and Peppers
Ingredients: 3 tablespoons butter; 1 red, yellow, or orange bell pepper; 1 red, yellow, or orange bell pepper; 1 red, yellow, or orange bell pepper; 1 onion; ⅛ teaspoon crushed red pepper flakes; 1 ½ cups (12 ounces) hard apple cider or beer; 1 ½ cups (12 ounces) hard apple cider or beer; 6 fresh or smoked bratwursts; 6 fresh or smoked bratwursts; 1 tablespoon coarse-grain mustard; 6 top-loading hot dog buns, split