In a large bowl, stir together the breadcrumbs and milk. Season with a big pinch of salt, a grind of black pepper and the allspice. Leave for a few minutes, until the breadcrumbs have soaked up the milk and formed a rough paste.
Add the ground pork and beef, grated onion and egg. Mix until evenly combined. With wet hands, roll into about 20 meatballs, each just smaller than a golf ball. Set aside.
Cut the potatoes into even chunks and place them in a saucepan. Cover with room-temperature water and add the fine sea salt. Bring to a boil, then reduce the heat and simmer for 10 to 15 minutes, until a fork slides through easily. Drain and set aside.
While the potatoes cook, heat the vegetable oil in a large non-stick skillet over medium heat. Fry the meatballs for about 3 minutes per side, until golden brown all over. Reduce the heat slightly and let them cook gently while you make the gravy and mash, until there's no pink in the center (160°F / 71°C).
For the gravy, melt the butter in a saucepan over medium heat. Whisk in the flour until it forms a paste. Gradually whisk in the cream, beef stock, onion powder and garlic powder. Add the brown sugar, bay leaf and browning or dark soy sauce, and simmer until thickened to your liking. Season with salt and pepper to your liking and remove the bay leaf.
Add the milk and butter to the drained potatoes and season with salt and black pepper. Blend with a hand blender, or mash with a potato masher, until smooth.
Divide the mashed potatoes between 4 bowls. Top with the meatballs, lingonberry jam, pickled cucumbers and gravy, then finish with fresh dill.