Soak breadcrumbs in milk for 5 to 10 minutes until the liquid is absorbed.
To a bowl add onion, egg, ground beef, all spice salt and pepper. Mix all the ingredients together with your hands and shape the meat mixture into small balls, less than an inch in diameter. If the mixture starts to sticks to your hands, wet them with cold water.
Heat a skillet with butter and extra virgin olive oil. Sauté the meatballs in 2 or 3 batches, turning them frequently to keep the meatballs from sticking. Drain them on paper towels.
Drain the excess olive oil and scrape off and discard any browned bits of meat that may be sticking to pan after the meatballs are done. To the same pan add butter and flour and stir until it browns. Quickly add a can of beef stock and bring to a boil, stirring constantly until gravy thickens.
Remove from the heat and serve immediately with the meatballs. For real Swedish Meatballs use Lingonberry preserves, but that is optional.