Preheat the oven at 400-degree F.
In a large mixing bowl, mix the ingredients for the meatballs, i.e., ground beef, sausage, onion, garlic, panko, egg, milk, herb seasoning, parmesan, basil, paprika, mustard powder, salt, and pepper.
Once mixed well, roll out the meatballs around 1-inch to 1 ¼ inch balls. That batter will make around 20 to 15 meatballs.
Grease the baking pan with 1 tbsp of butter and place the meatballs on the pan.
Let them bake for 15 to 20 minutes until cooked and browned.
Once cooked, let them rest and sit ahead.
Add the remaining 2 tbsp of butter to the Dutch oven and let it heat on medium heat.
Once the butter is foamy, sauté onions until translucent.
Now, add garlic and cook for a minute until fragrant.
Pour in the chicken stock, crushed tomatoes, diced tomatoes, and mix.
Season with Italian herb seasoning and pepper.
Once the sauce starts to shimmer, let it cook for 10 to 12 minutes.
Let the sauce thicken, and it is more like coating consistency.
Drop the meatballs in the sauce and cook them for 5 minutes until sauce coats the meatballs.
Serve hot and enjoy!