buttered egg noodles or mashed potatoes, for serving
1 tsp. yellow mustard
1/2 cup sour cream
1 3/4 cups beef or chicken broth, low sodium if possible
2 tbsp. flour
1/2 tbsp. Worcestershire sauce
1/2 tbsp. oil
1/4 tsp. garlic powder
1/4 tsp. ground allspice
1/4 tsp. ground nutmeg
1 tsp. salt
1/2 tsp. black pepper
1 large egg
1 1/4 pounds lean ground beef
3 tbsp. milk
2 slices bread, torn into small pieces
5 tbsp. butter
1 small onion, finely chopped