Mix the meatball mixture

• Combine the ground beef, ground pork, panko, milk, half the parmesan, egg, garlic, parsley, salt and pepper.
• Mix until just combined; the mixture should be moist, adding more milk if needed.

Form the meatballs

• Scoop about 2 tablespoons of mixture per meatball.
• Roll into 1 1/2 inch balls with damp hands.

Sear the meatballs

• Heat the oil in a skillet over medium heat.
• Sear the meatballs in batches, turning every 2 minutes until browned.

Assemble the casserole

• Spread 1 cup of marinara in a 9x13 dish.
• Add the meatballs and cover with the remaining sauce.
• Top with the remaining parmesan and the mozzarella.

Bake

• Cover with foil and bake at 400°F until the meatballs reach 165°F, the cheese is melted and the casserole is bubbling.