Swedish Meatball Soup

Combine 1 cup onion and 1 tablespoon water in a large Dutch oven. Cook over medium heat, stirring occasionally, until the onion softens and browns, about 6 minutes. Transfer to a large bowl; let cool for 5 minutes.

Stir eggs, panko, milk, 2 teaspoons Worcestershire, 3/4 teaspoon pepper, 1/2 teaspoon allspice and 1/4 teaspoon nutmeg into the onions in the bowl. Let the panko soak for 3 minutes. Add ground beef; mix gently until well incorporated. Shape the mixture into 30 meatballs (about 1½-inch diameter; 1 rounded tablespoon each); place on a parchment-paper-lined baking sheet. Refrigerate, uncovered, until slightly firm, about 20 minutes.

Heat 1 tablespoon oil in the Dutch oven over medium-high heat. Working in 2 batches, sear the meatballs, carefully stirring occasionally, until browned all over, about 10 minutes. Transfer the browned meatballs to a baking sheet. (Do not wipe the pot clean.)

Reduce heat to medium; add the remaining 2 tablespoons oil and the remaining 1 cup onion. Cook, stirring often and scraping the bottom of the pot to loosen browned bits, until the onion begins to soften, 3 to 4 minutes. Add flour; cook, stirring constantly, 1 minute. Gradually stir in broth. Add potato, mushrooms, vinegar, sugar, mustard, salt, and the remaining 2 teaspoons Worcestershire, 1/4 teaspoon each pepper and allspice and 1/8 teaspoon nutmeg; stir to combine.

Return the seared meatballs to the pot. Cover, reduce heat to medium-low and simmer until the potato is tender and meatballs are cooked through, 12 to 15 minutes.

Reduce heat to low; stir in cream. Cook, stirring occasionally, until the cream is heated through and the soup is slightly thickened, about 5 minutes. Top with parsley and serve.