Soak the breadcrumbs in the milk for 5 minutes. Stir in the cooled onion, egg, 1 1/4 teaspoons salt, allspice, nutmeg, and pepper until a loose paste forms. Add the beef and mix with your hands for about 45 seconds, until the mixture looks even and slightly sticky.

Scoop 1 1/2 tablespoons of mixture and roll it between damp palms into a ball about 1 1/4 inches wide. Set 36 meatballs on the parchment-lined sheet and chill for 10 minutes until smooth and set.

Wipe out the skillet, add the oil, and heat over medium-high for 2 minutes until it shimmers. Brown the meatballs in 3 batches of 12, turning every 90 seconds, for 5 to 6 minutes per batch, until deep golden brown on every side. Move them to a clean plate.

Pour off all but 1 tablespoon of fat. Add 2 tablespoons butter and the flour, then whisk for 90 seconds until the paste is pale gold and smells nutty.

Whisk in the broth a splash at a time, scraping up the brown bits. Stir in the cream, 1/2 teaspoon salt, and lemon juice, then simmer over medium heat for 3 minutes until the gravy coats the back of a spoon.

Return the meatballs and their juices to the skillet. Simmer over medium-low heat for 8 to 10 minutes, turning once, until a thermometer in the center of a meatball reads 160°F. Keep to small bubbles, not a rolling boil.

Take the skillet off the heat and rest for 5 minutes until the gravy is thick and glossy. Top with parsley and serve with lingonberry jam.