In a white ceramic mixing bowl, pour the whole milk over the breadcrumbs and let them sit for 5 minutes until soft and paste like. Add the ground beef, ground pork, grated onion, egg, garlic, allspice, nutmeg, 1 1/4 teaspoons salt and pepper, then mix with your hands just until combined; the mixture should look even but not sticky.

Scoop the mixture with a small cookie scoop or tablespoon and roll between your palms into balls about 1.5 inches wide. Set them on a pale wood board as you go; you should end up with 22 to 24 meatballs.

Melt 3 tablespoons butter in the cream Dutch oven over medium heat until it foams. Working in two batches so the pan is not crowded, brown the meatballs on all sides, turning every 2 minutes, about 6 to 8 minutes per batch; they should be deep golden outside but still pink in the center. Transfer them to a plate.

Leave about 2 tablespoons of fat and browned bits in the cream Dutch oven, pouring off any extra. Add the remaining 3 tablespoons butter, let it melt, then whisk in the flour and cook for 1 minute, stirring, until it smells toasted and turns pale gold.

Pour in the beef stock in a slow stream, whisking the whole time to work out lumps and lift the browned bits from the bottom of the pot. Bring to a gentle simmer; it should thicken slightly within 2 to 3 minutes.

Stir in the heavy cream and Worcestershire sauce. Simmer uncovered for 3 to 4 minutes, stirring occasionally, until the gravy is smooth and coats the back of a spoon without running straight off it.

Return the browned meatballs and any juices on the plate to the cream Dutch oven. Cover partially and simmer gently for 10 to 12 minutes, turning once halfway through, until an instant read thermometer in the center of a meatball reads 165°F (74°C).

Turn off the heat and stir in the lemon juice. Taste the gravy and add more salt and pepper if needed; the lemon should barely register, just enough to keep the cream from tasting flat.

While the meatballs brown, bring a large pot of generously salted water to a boil and add the potato chunks. Boil for 15 to 18 minutes, until a knife slides into a piece with no resistance.

Drain the potatoes well and return them to the same pot. Add the butter and warmed milk, then mash with a potato masher until smooth; season with salt to taste.

Let the meatballs rest in the gravy, off the heat, for 5 minutes before serving; the gravy thickens slightly more as it sits and clings better to each meatball.

Spoon the mashed potatoes onto a white ceramic platter, spreading a shallow well in the center. Arrange the meatballs and gravy over the potatoes, add a generous spoonful of lingonberry or cranberry sauce on the side, and scatter the parsley over the top.