Mix the Meatballs
In a large mixing bowl, combine ground beef, pork, breadcrumbs, milk, egg, garlic, Parmesan, parsley, salt, and pepper. Use your hands or a wooden spoon to gently mix until just combined — overmixing can make the meatballs tough.
Form the Meatballs
Roll the mixture into 1½-inch balls (about golf ball size). Place them on a parchment-lined baking sheet.
Brown the Meatballs (Optional but Recommended)
Heat a skillet over medium heat and add a drizzle of olive oil. Brown the meatballs on all sides for about 1–2 minutes per side.
If you’re using frozen meatballs, skip this step and go straight to the crockpot.
Layer in the Crockpot
Add the diced onions and minced garlic to the bottom of your slow cooker. Then layer in the meatballs, followed by the crushed tomatoes, tomato sauce, tomato paste, Italian seasoning, olive oil, sugar, and a pinch of salt and pepper.
Give it a gentle stir so the sauce is evenly distributed over the meatballs.
Cook on Low and Slow
Cover the crockpot and cook on LOW for 6–7 hours or HIGH for 3–4 hours, until the meatballs are tender and cooked through.
You’ll know they’re done when the sauce is thick, rich, and the meatballs are juicy enough to cut with a spoon.
Finish and Serve
Before serving, stir in a handful of fresh parsley or basil, and taste for seasoning.
Serve the meatballs straight from the crockpot with pasta, mashed potatoes, or even tucked inside crusty rolls for the best meatball subs you’ve ever had.