Preheat the oven to 375°F. In a large bowl, combine the ground beef, breadcrumbs, 1/4 cup milk, onion, 2 minced garlic cloves, 2 tablespoons Italian seasoning, 1/4 cup Parmesan, salt, and pepper. Mix until just combined, then shape into a loaf and place in a loaf pan.
Bake the meatloaf for 45 to 50 minutes until it reaches an internal temperature of 160°F. While it bakes, heat the olive oil in a saucepan over medium heat. Add the remaining minced garlic clove and cook for 1 minute, then stir in the crushed tomatoes and 1 teaspoon Italian seasoning. Simmer the marinara for 15 minutes.
In a separate pot, bring the chicken broth to a boil. Slowly whisk in the cornmeal. Reduce heat to low and cook, stirring often, for 20 minutes until thick. Stir in the remaining 1/2 cup milk, butter, and 1/4 cup Parmesan until smooth and creamy.
Let the meatloaf rest for 5 minutes after baking. Slice it and spoon the marinara over the top. Serve each portion with a scoop of the creamy polenta on the side.