Transylvanian Beef Stew with Pumpkin Goulash

Name: Transylvanian Beef Stew with Pumpkin Goulash
Ingredients: 1/2 tablespoon unsalted butter; 1 tablespoon olive oil; 2 1/2 cups thinly sliced red onion; 1 1/2-2 pounds beef stewing meat (cut into 1-inch pieces); 1/3 cup all-purpose flour; 2 1/2 tablespoons sweet Hungarian paprika; 1 1/2 teaspoons caraway seeds; 2 cups beef stock; 2 tablespoons tomato paste; 1 large green bell pepper, stem end and membranes removed, sliced (2 cups); 1/4 cup sour cream, optional; 2 tablespoons chopped fresh dill, plus extra sprigs for garnish; 1 recipe for Pumpkin Polenta (recipe follows)