Place 1/4 cup of mozzarella on the bottom of a 12-ounce coffee mug. Top with half the marinara, and carefully place cooked rigatoni upright in the mug, making sure it is a very tight fit. Top with remaining marinara and cover with remaining mozzarella. Bake for 20 to 25 minutes until cheese bubbles up and turns golden. Place a saucer or small plate on top of the mug and flip over. Top with basil and serve immediately.