In a large bowl, mix together the milk, breadcrumbs, egg, cinnamon, nutmeg, salt, garlic salt, Worcestershire sauce, and mustard. Let the mixture sit for 5 minutes to allow the breadcrumbs to absorb the liquid.

Add the Wagyu beef, and caramelized onions. Gently mix until just combined—do not overwork the meat.

Roll the mixture into evenly sized meatballs (about 1 inch in diameter).

Heat butter in a large skillet over medium heat. Add the meatballs in batches and cook until browned on all sides and cooked through (about 8–10 minutes). Remove and set aside.

In the same pan, add the chopped onions and sauté until softened. Pour in the chicken stock and let it simmer for 5 minutes, allowing the flavors to meld.

Lower the heat and stir in the heavy cream. Let it simmer gently for another 3–5 minutes until slightly thickened.

Add the cooked meatballs back into the pan, spooning the sauce over them to coat. Let them simmer for a couple of minutes.

Plate the meatballs over mashed potatoes with broccolini on the side. Spoon extra sauce over the top, then garnish with lingonberry jam, pickled cucumbers, and fresh parsley.