Make meatballs: In a medium bowl, stir together bread crumbs and milk. Add 1/2 tsp. each salt and pepper, 1/4 tsp. nutmeg, 1 tbsp. parsley, the pork, and beef. Mix gently but thoroughly with your hands. Scoop mixture by slightly rounded teaspoons and roll into small balls, dipping spoon occasionally in water to keep mix from sticking.
Heat a large nonstick frying pan over medium heat. Add 1 tbsp. oil and swirl to coat. Brown half of meatballs, turning once and reducing heat if they start browning too fast, 5 to 8 minutes. Transfer to a plate. Repeat with remaining oil and meatballs. Meanwhile, continue with soup.
Melt butter in a large pot over medium heat. Add carrots and leeks and cook, stirring, until leeks are soft but not browned, 8 to 10 minutes.
Stir in cabbage and remaining 1/4 tsp. each salt and pepper and cook until slightly wilted, 3 to 5 minutes. Add broth, cover, and bring to a simmer over high heat. Reduce heat and simmer until cabbage is quite tender, about 20 minutes.
Gently stir browned meatballs into soup and cook, stirring occasionally, until meatballs are cooked through and flavors are blended, about 5 minutes. Stir in cream, 3 tbsp. parsley, and remaining 1/8 tsp. nutmeg and ladle into bowls. Sprinkle with remaining 1 tbsp. parsley.
*Choose ground beef with at least 20% fat for the juiciest meatballs.