Preheat an oven to 200F (95C). Place the bread pieces in a small mixing bowl and combine with the milk. Set aside.

Melt 1 tablespoon of the butter in a 12 inch straigh-sided pan over medium heat. Add a pinch of salt and the onion. Saute until the onions are soft. Remove pan from the heat and set aside.

In a large bowl, combine the milk and bread mixture, pork, beef, salt, yolks, onions, nutmeg, pepper and allspice. Use an electric mixer to beat on medium speed for 1 to 2 minutes.

Use hands to shape 1 ounce portions of meat mixture into balls. Melt the remaining butter in a medium skillet over medium-low heat and brown the meatballs on all sides, about 7 to 10 minutes.

Transfer the meatballs to a baking dish and place in the preheated oven. Once meatballs are cooked through, set the heat on the skillet to low and add the flour, and whisk until browned, about 1 to 2 minutes. Slowly add the broth and whisk until it begins to thicken. Add the cream, and whisk until desired consistency is reached.

Remove meatballs from oven, pour the gravy mixture over it, and serve.