Put a little olive oil in a pan and cook the onion down a bit so it releases its moisture.
Form the meatballs:
In a large bowl, combine the beef, pork, egg, breadcrumbs, onion, onion powder, garlic powder, allspice, nutmeg, and some salt and pepper. Cook a pinch of the mixture and taste the seasoning and adjust before forming the meatballs.
Cook the meatballs:
Form the meat mixture into meatballs, whatever size you like. Add a tbsp of oil to the pan and begin to brown the meatballs on all sides. Cook in batches so you don't overcrowd the pan and steam them. Remove them to a plate.
Add the butter to the skillet and melt it. Add the flour and stir for a few minutes to brown it up a bit. Slowly add the broth while whisking to prevent lumps. Stir in the sour cream, then add the meatballs back in and continue to cook until they are fully cooked through (about 10-15 minutes). The meat will also impart some great flavor to the gravy as it simmers.
Plate up the pasta and spoon the meatballs and gravy over the top. Add chopped parsley if you like, or parmesan. Serve with the jam on the side.