Using a cutting board, chop onion into fine pieces.
Chop and mince 1 clove of garlic.
In a large saucepan heat oil over moderately high heat. Add onion and garlic and cook 2 to 3 minutes, stirring constantly, until onion is translucent.
Stir in tomatoes, tomato paste, basil and 1/2 tsp. of the salt. Bring to a boil; then reduce heat to moderately low, cover pan and simmer 20 minutes, stirring occasionally.
In a medium sized bowl mix cheeses, egg, pepper, cloves and the remaining 1/2 tsp. salt.
Heat oven to 350 degrees. Cover the bottom of a 2 1/2 qt. oblong baking dish with about 1 cup of the tomato sauce; sprinkle with half the mostaccioli. Cover with half the cheese mixture, 2 more cups tomato sauce and remaining mostaccioli. Top with remaining cheese and sauce.
Bake at 350 for 20 to 25 minutes, until sauce is bubbling and cheese is melted.