Adding sugar doesn't help; longer cooking only makes it worse. Bitter tomato sauces happen for one of two reasons, the tomatoes taste bitter when raw and/or the sauce is overcooked.

Try experimenting with these emergency tactics. Reheat two cups sauce with a half-teaspoon baking soda, which may neutralize the bitterness. Or reheat a few cups, swirling in chunks of unsalted butter until it is barely melted and creamy. See if the butter mellows out the bitterness.

If neither helps, toss the sauce. Don't subject yourself to a bad sauce. Chalk it up to learning, and check for good tomatoes in the market next time.

Otherwise, try whole, canned tomatoes by Muir Glen, Red Gold or Hunt's. They won't let you down.