For the meatballs : mix both types of minced meat, soaked bun, chopped onion, egg, breadcrumbs and knead smooth meat mixture, add salt and pepper to taste, optionally, you can add a little anchovy paste. Form meat mixture into round meatballs. Add peeled onion, allspice, bay leaf and black pepper in the broth, bring to a simmer , salt and place meatballs into hot broth, simmer gently for 10 minutes, remove all spices and onion from broth, let meatballs rest in broth for another 10 minutes. Melt the butter over medium heat in a saucepan, add the flour, fry gently and pour the broth in a thin stream, stirring constantly. Add capers and cream, remove from heat, season with sugar and lemon juice to taste, salt and pepper. Add egg yolk and place meatballs in the sauce and sprinkle with parsley.