Bring to boil and then reduce heat and allow to simmer for at least 30 minutes.
Brush outsides with butter (no substitutes!) (I add minced garlic to the butter first just for extra deliciousness!)
Spread prepared pesto on one side of bread
Place shredded mozzarella and parmesan cheese on top of pesto
Bake sandwiches on crinkled tinfoil on a baking sheet for 30-40 min at 300 degrees, flipping once. Or can toast on griddle.