Bring a large pot of water to a boil, add 1 1/2 teaspoons salt, and cook the macaroni for 1 minute less than the package directs.
Reserve 1/2 cup pasta water and drain the macaroni.
Crush the stewed tomatoes with a spoon in the pot and simmer them with the butter, sugar, pepper and remaining salt for 8 minutes.
Stir in the macaroni and cook for 3 to 4 minutes until it is tender and has absorbed some tomato juice.
Add the reserved pasta water 2 tablespoons at a time only if the mixture looks dry rather than saucy.
