Combine the breadcrumbs, cream, Dijon, milk, egg, salt, and pepper. Let the mixture soak for 10 minutes, then add the ground beef and pork. Roll the mixture into about 34 balls and place on a parchment-lined baking sheet. Cover in plastic and store in the refrigerator for 1 hour. To keep the meatballs from not falling apart.
Heat the veal stock in a medium saucepan over high and reduce by half, about 10 minutes. Add the heavy cream and reduce over medium until it is just over 2 cups, about 1 hour. Add the lingonberry jam and cook 5 minutes longer over low heat, then season with salt and pepper.
Boil the potatoes, drain, then return the potatoes to the saucepan and mash. Add the milk, nutmeg and butter and stir to combine. Season with salt and white pepper.
Fry the meatballs, turning them until they are browned all over, approximately 4 minutes. Add 3 tablespoons butter and continue cooking until cooked through, 3 to 4 minutes more.
To serve, divide the potato purée among plates and top with meatballs. Add generous amounts of the sauce and serve with the fresh lingonberries and the pickled cucumbers.