Soak the panko: Stir the panko and milk together in a large bowl and let it sit 5 minutes, until the crumbs have drunk up all the milk and look like wet sand. Heat the oven to 400°F and line a rimmed sheet pan with parchment.

Mix and roll: Add the ground beef, ground pork, egg, parmesan, minced garlic, parsley, Italian seasoning, salt, and pepper to the soaked panko. Mix with your hands just until you can't see streaks of egg anymore, then stop. Roll into 24 balls about 1 1/2 inches across and space them out on the sheet pan.

Bake the meatballs: Bake for 20 minutes, until browned on top and a thermometer pushed into the center of the biggest one reads 160°F. Ground beef and ground pork are both safe at 160°F.

Simmer in the sauce: While the meatballs bake, warm the marinara in a large skillet or pot over medium-low heat. Slide the baked meatballs in, spoon sauce over them, and let them simmer gently for 10 minutes so they soak it up.

Toast the rolls: Mash the softened butter with the grated garlic and spread it on the cut sides of the rolls. Set them cut side up on a sheet pan and broil 1-2 minutes, until the edges are golden. Watch them closely.

Build and broil: Lay one slice of provolone in the bottom of each roll. Add 4 meatballs with sauce, then top with a second slice of provolone. Broil 2-3 minutes, until the cheese is melted and bubbling with a few browned spots. Scatter the basil over the top and serve.