In a large mixing bowl, combine ground beef and ground pork with finely chopped parsley, allspice, nutmeg, grated onion, kosher salt, pepper, minced garlic, panko breadcrumbs, and eggs. Mix gently and form into golf ball-sized meatballs, about 30-35 total.

Heat olive oil in a large skillet over medium heat. Add meatballs in batches, cooking about 3 minutes on each side until golden brown. Remove and set aside.

In the same skillet, reduce heat to medium-low, add unsalted butter until melted, then whisk in flour until smooth. Gradually pour in beef stock while whisking to avoid lumps. Season with salt, pepper, allspice, nutmeg, and heavy cream; cook until thickened, about 3-5 minutes.

Add browned meatballs back into the gravy, coating thoroughly. Simmer on low heat for about 10 minutes.

Serve the Swedish meatballs warm over fluffy mashed potatoes or egg noodles, optionally with lingonberry jam.