Preheat oven to 400 degrees. Spray a rimmed baking sheet with non-stick spray.
Add the ground beef, pork, bread crumbs, Parmesan, parsley, garlic, onion, and egg to a large mixing bowl and combine well with your hands. Do not overmix.
Separate the mixture into 12 equal sized chunks and roll into meatballs.
Place meatballs on prepared baking sheet and bake for 10 minutes.
To make the sauce:
Add all of the sauce ingredients to a 6 quart slow cooker and stir well to combine.
Remove the meatballs from the oven and place in the slow cooker with the sauce.
Cover and cook on low for 4 hours.
To make the subs:
Open the hoagie rolls and butter the insides of each roll.
Sprinkle evenly with the garlic salt.
Place opened hoagie rolls on a large baking sheet under the broiler and broil until as toasted as you’d like. Keep a close eye on the bread as it will go from toasted to burnt very quickly.
Remove the bread from the oven and add 3 meatballs to each sandwich. Top with a spoonful of sauce.
Top each sandwich with 2 slices of fresh mozzarella. Return to the broiler for 1 minute to let the cheese melt a bit.
Sprinkle the sandwiches with fresh parsley and serve.
Video
Notes
Meatballs: We love the flavor that the ground pork gives to these meatballs, but you can use all beef if preferred.Sauce: We use and love Rao's sauce, but any jarred sauce will work fine. The red pepper flakes do not make this spicy and the sugar does not make it sweet. Both just work to balance the sauce. Hoagie Rolls: We like a good quality, crusty roll for these sandwiches. Toasting is optional, but the crispy edges and warm bread really make these special. Cheese: Fresh mozz is the key to my heart, but you can easily sub sliced or shredded cheese here. Use what you've got!