Cut the bread in pieces and lay them in a bowl with milk, set aside.
Melt in a frying pan 1 tbsp of butter, add the onion and a pinch of salt and cook until the onions are soft. Remove from the heat and set aside.
In the bowl with the bread and milk mixture add the meat, egg yolks, 1 tsp of salt, black pepper, allspice, nutmeg and the onions.
Mix all this together for around 2 minutes.
Using your hands to shape the meatballs into balls from around the size of a walnut.
Heat up the remaining butter in a frying pan, add the meatballs and sauté until they're golden brown at all sides.
Remove the meatballs and lay them on a baking dish (previously covered with baking paper) and bake them (in a previously preheated oven) at 180°C for 15 minutes or until well done.
In the meanwhile decrease the heat from the frying pan and add the flour to it, then whisk until lightly browned and gradually add the beef stock.
Keep mixing until the sauce begins to thicken.
Add the cream and continue to cook until the gravy reaches the perfect consistency.
Remove the meatballs from the oven, cover them with the gravy and serve.