Step 1

In a large pot of boiling salted water, cook pasta according to package instructions; drain well.

Step 2

In a large bowl, combine ground beef, ground pork, Panko, egg yolks, green onions, parsley, allspice and nutmeg; season with 1 teaspoon salt and 1/2 teaspoon pepper. Using a wooden spoon or clean hands, stir until well combined. Roll the mixture into 1-to-1-1/4-inch meatballs, forming about 24 meatballs.

Step 3

Heat olive oil in a large skillet over medium high heat. Add meatballs, in batches, and cook until all sides are browned, about 2-3 minutes. Transfer to a paper towel-lined plate; set aside.

Step 4

Melt butter in the skillet. Whisk in flour until lightly browned, about 1 minute. Gradually whisk in beef stock and cook, whisking constantly, until slightly thickened, about 3-5 minutes.

Step 5

Stir in meatballs and cook, stirring occasionally, until heated through and thickened, about 5 minutes. Stir in pasta and sour cream until heated through, about 2-3 minutes; season with salt and pepper, to taste.

Step 6

Serve immediately.