In a medium bowl, gently combine the beef, onion, breadcrumbs, egg, spices and salt and pepper with your hands, and shape it into 1-inch balls.
In a drizzle of oil in a heavy (cast iron is great) skillet set over medium-high heat, cook the meatballs, rolling them around as you need to, until deep golden and crusty and cooked through. With a slotted spoon, transfer them to a bowl and set aside.
Drain the excess fat from the pan, leaving about a tablespoon. Add the butter (if you like, or just leave the drippings in the pan) and the flour, and whisk to combine. Add the stock and stir, scraping up the browned bits from the bottom of the pan, until the mixture boils and thickens. Whisk in the sour cream and stir until it has the texture of creamy gravy. This whole process will only take a few minutes.
Return the meatballs to the pan and roll them around to coat. Serve with cranberry or lingonberry sauce.