This is a very traditional German comfort food, and easy to make. Normally this recipe uses equal parts beef, pork, and veal.
1 – 1 1/2 lbs cooked, frozen meatballs
2 cups water
1/2 tsp salt
1 bay leaf
3 tbsp butter
2 tbsp flour
1 tsp prepared mustard
1 egg yolk
Put frozen meatballs into pot; add water, salt, freshly ground pepper, and bay leaf.
Bring to boil, lower heat, cover, and simmer for about 15 – 20 minutes.
Meatballs should be hot inside.
Drain meatballs, reserving liquid. Cover meatballs to keep hot.
Melt butter in fry pan. Add flour and stir well. (Do not brown flour)
Add reserved liquid, stirring well. Cook, stirring constantly, until thickened.
Remove from heat. Add some of the sauce into the egg yolk (in a small bowl). Stir and return to sauce in fry pan. Simmer about 2 minutes, adding a bit of water if necessary if too thick.
Add capers and mustard. Season with salt and pepper.
Return meatballs to sauce, stir.