Bratwursts with Braised Red Cabbage and Potatoes

Name: Bratwursts with Braised Red Cabbage and Potatoes
Ingredients: 1 pound small red potatoes , unpeeled, halved; 1 1/2 teaspoons table salt , divided, plus salt for cooking potatoes; 4 tablespoons unsalted butter , softened, divided; 1/2 teaspoon pepper , divided; 2 pounds bratwurst; 1/2 head red cabbage , halved, cored, and sliced 1⁄4 inch thick (6 cups); 1 Gala apple , cored and cut into 1⁄2-inch pieces; 1 tablespoon packed brown sugar; 1 1/2 teaspoons minced fresh rosemary; 2 tablespoons cider vinegar