Serious Eats - seriouseats.com

I always put tomatoes through a food mill (smallest holes) to remove skins and seeds, which contribute the the bitter flavor people comment about. Nearly everyone I know puts sugar in their tomato sauce, even people "off the boat". Whenever I hear this, I know they aren't straining the tomatoes. It's a lot of work and makes a big mess, but I wouldn't make tomato sauce without doing it.