Preheat your oven to 410°F (210° C).
In a large bowl, mix the ground beef, pork, and veal.
Add the Italian breadcrumbs, grated Romano cheese, eggs, milk, fresh parsley, minced garlic, salt, and black pepper.
Use your hands to mix until everything is well combined.
Form the mixture into 1.5-inch meatballs and place them on a baking sheet lined with parchment paper.
Heat the olive oil in a large skillet over medium-high heat.
Add the meatballs and cook until golden brown on all sides.
Transfer the browned meatballs to a baking dish.
In the same skillet, add the finely chopped onion and cook until softened.
Add the minced garlic and cook for another minute.
Stir in the can of tomatoes, bay leaf, and red pepper flakes.
Bring the sauce to a boil, then reduce the heat and simmer for 5 minutes.
Cover the meatballs with the marinara sauce and bake in the preheated oven for 25-30 minutes.