In a large bowl, combine ground beef, bread crumbs, egg yolks, nutmeg and minced onion; season with salt and pepper, mix until well combined.

Roll the ground beef mixture into about 15 golf ball sized meatballs.

Add 2 tablespoons of olive oil to the skillet. Add meatballs and cook until all sides are browned.

Transfer to a plate lined with paper towel.

To make the gravy, melt butter in the skillet. Whisk in flour until lightly browned.

Gradually whisk in beef broth and Worcestershire sauce, stirring constantly until slightly thickened.

Stir in heavy cream; season with salt and pepper, to taste.

Stir in meatballs, cook until thickened.

Serve warm over mashed potatoes.