Add sausage, diced white onion, Italian bread crumbs, black pepper, salt, milk and ground sage (if using it) together in a bowl and use your hands to mix together well.
Roll into roughly 2 tablespoon or 2-3 inch meatballs, this will make 16.
Roll meatballs in flour.
Heat a skillet to medium high heat with the olive oil in the pan.
Brown each meatball evenly on each side then place in a 8 x 8 baking pan.
Bake for 25 minutes or until internal temperature is 165 F.