Beef Stroganoff Sauce with Meatballs

Ingredients (14)

• ✓ ½ teaspoon vegetable oil, or as needed
• + 1 pound ground sirloin add to pantry
• + 3 tablespoons Worcestershire sauce add to pantry
• + 1 egg add to pantry
• ✓ ⅓ cup dry bread crumbs
• + ½ small onion, chopped add to pantry
• + salt and ground black pepper to taste add to pantry
• + salt and ground black pepper to taste add to pantry
• + ¼ cup butter, divided add to pantry
• + 1 (16 ounce) package mushrooms, sliced add to pantry
• + 2 tablespoons all-purpose flour add to pantry
• + 1 (10.5 ounce) can beef broth add to pantry
• + 1 teaspoon ground mustard add to pantry
• + ⅓ cup sour cream add to pantry