In a 12-inch metal pan over medium heat, melt 1 tablespoon of the butter. Add the chopped onion, and a pinch of the salt cook until the onions are soft. Add garlic to the pan and cook 2 minutes. Remove the metal pan from the heat and set aside.
In a large bowl, combine the breadcrumbs and milk mixture, ground chuck, pork, egg yolks, kosher salt, black pepper, allspice, nutmeg, cooked onions, and minced garlic.
Form the meatballs into 1×1 in size and place on a metal sheet pan till needed.
Heat the remaining butter and olive oil in a sauté pan over medium-low heat. Add the formed meatballs and cook until lightly browned on all sides, about 8 minutes. Remove the meatballs from the metal pan to a platter using a slotted spoon, reserve the meatballs on the side until needed
Gradually add the beef stock, all-purpose flour, sour cream, and Worcestershire sauce into a crockpot on the heat setting of high and whisk until joined. Place the cooked meatballs in the crock-pot and cook on *cook on high for at least 1 hour* then on low 8 hours, stirring here and there. Season with more kosher salt and pepper if desired.
Serve the Swedish Meatballs by themselves as an appetizer, or over egg noodles