Beef Stroganoff Sauce with Meatballs Recipe

Ingredients

• 1/2 teaspoon vegetable oil, or as needed
• 1 pound ground sirloin
• 1/2 small onion, chopped
• 1/3 cup dry bread crumbs
• 3 tablespoons Worcestershire sauce
• 1 egg
• salt and ground black pepper to taste
• 1/4 cup butter, divided
• 1 (16 ounce) package mushrooms, sliced
• 2 tablespoons all-purpose flour
• 1 (10.5 ounce) can beef broth
• 1 teaspoon ground mustard
• 1/3 cup sour cream