Preheat oven to 200 degrees F.
Place torn bread in a small mixing bowl and cover with milk. Set aside to soak. Once the liquid is absorbed blend bread in food processor.
In a medium skillet over medium heat, melt 1 tablespoon of butter. Add onion and a pinch of salt and saute until the onions are softened. Remove from the heat and set aside.
In the bowl combine the bread mixture, ground beef, ground pork, egg yolks, remaining salt, pepper, allspice, nutmeg, and sauteed onions. Stir until well mixed.
Divide into 50 pieces- shape into balls.
Heat 2 TBSP butter in the saute pan over medium-low. Add meatballs and saute until golden on all sides, about 7 to 10 minutes. Remove to an ovenproof dish and place in the warmed oven.
When all of the meatballs have been cooked, decrease the heat to low. Drain all but 2 TBSP fat from skillet and whisk in flour. Whisk until the flour is lightly browned, approximately 1 to 2 minutes. Gradually add beef broth and whisk until mixture begins to thicken. Add heavy cream and continue to cook until the sauce reaches the desired consistency. Remove the meatballs from the oven, cover with sauce and serve hot.