Crockpot Swedish Meatballs {IKEA Copycat}

Name: Crockpot Swedish Meatballs {IKEA Copycat}
Prep time: 20 min
Cook time: 6 h
Total time: 6 h 20 min
Cuisine: European
Ingredients: 1 lb extra-lean ground beef; 1/4 cup breadcrumbs; 1 egg; 1 yellow onion (grated); 2 cloves minced garlic; 1/2 tsp each salt and pepper; 1/4 tsp nutmeg; 1/4 tsp allspice (or just use another 1/4 tsp nutmeg); 2 tbsp butter; 2 tbsp flour; 2 cups beef broth; 1/4 cup sour cream; 3 White potatoes (chopped); 1 tbsp butter; Salt & pepper (to taste); 2 cups green peas (canned or frozen); Lingonberry jam (optional, to serve); 1/4 cup fresh parsley (finely chopped; optional garnish)