1In a large skillet over medium heat, melt 4 Tbsp of unsalted butter.
2Add 1 finely diced onion and sauté until fragrant.
3Stir in 1 Tbsp of minced garlic and cook for 1 minute.
4Whisk in 2 Tbsp of all-purpose flour until the mixture thickens.
5Whisk in 2 cups of beef stock or broth in small batches, whisking constantly for 3–5 minutes.
6Add the following seasonings: 1/2 tsp salt, 1/4 tsp garlic powder, 1/4 tsp onion powder, a dash of ground allspice seasoning, 1 tsp Dijon mustard, 1 tsp Worcestershire sauce, 2 Tbsp sour cream, 1/4 cup heavy whipping cream, 1 Tbsp of dried parsley, and a dash of ground nutmeg.
7Stir to evenly combine all ingredients, then taste and add more salt/pepper/spice if preferred.
8Add 1–2 cups of uncooked frozen or homemade meatballs to the sauce, ensuring all are evenly coated.
9Cover and let simmer for 25 minutes, or until the meatballs are fully cooked.
10Serve the meatballs and sauce over mashed potatoes.