Slow Cooker Meatballs in Tomato Sauce – Tender, Juicy & Set-It-and-Forget-It

1½ lbs ground beef or beef/pork mix

¾ cup breadcrumbs

⅓ cup milk

1 egg

¼ cup grated Parmesan

2 garlic cloves, minced

¼ cup minced onion

1½ tsp Italian seasoning

¾ tsp salt, ½ tsp pepper

1 (28 oz) can crushed tomatoes

1 (15 oz) can tomato sauce

2–3 garlic cloves, minced

1 tsp Italian seasoning

½ tsp salt

Pinch of sugar (optional)