Melt the butter in a medium skillet over medium meat. When the butter is foamy, add the onion and garlic and cook, stirring frequently, until softened, 5 to 7 minutes. Transfer to a large bowl. Add the ground pork, ground beef, breadcrumbs, allspice, nutmeg, eggs, salt, and pepper.
Using your hands, blend meatball mixture until well combined. Scoop out into 2 tablespoon portions (slightly smaller than a golf ball), then roll and shape. Set meatballs onto a baking sheet lined with parchment.
Bake meatballs for 10 minutes. While the meatballs are in the oven, make the sauce.
In a large skillet, melt the butter over medium-low heat. When the butter is foamy, whisk in the flour. Cook, whisking constantly, until the mixture cooks to a light brown color and turns very foamy, about 3 minutes.
Gradually whisk in the stock, followed by the Worcestershire and mustard. Whisk in the cream, salt, and pepper until smooth. The sauce will be thick. Remove from the heat.
With the meatballs still in the oven, turn on the broiler setting. Brown the meatballs for about 5-10 minutes.
When done, remove the meatballs from the oven. Check the sauce. If it’s too thick, whisk in some more beef stock to get it to the right consistency.
Toss the meatballs in the sauce and serve immediately with cocktail picks and a side of lingonberry or cranberry preserves.
Note - This recipe can also be made by heating pre-cooked, frozen meatballs and adding to the sauce.