This was put on another line but don't remember where, so I'll repeat (someone else here at DC does something very similar).
Halve tomatoes. This, believe it or not, works better if you cut across the equator rather than longitudinal. Do a cursory seeding with your thumbs, putting the seeds into a sieve over a bowl to drain. This keeps the resultant sauce from being too watery.
Place on a rimmed baking sheet along with cloves of garlic, slices of onion, a pepper or two. S&P. Bake at about 400 for about an hour. You are not trying to totally dehydrate, just to dry up enough so the resultant sauce will be thick and rich. When they cool, I put through my food mill, but pressed through a China cap or sieve will work.
If you have fresh basil and oregano, add at this time and freeze. If you'd rather use for chili or other Mex dishes, leave out the basil. Dried herbs can go in before roasting.
When you thaw, sometimes there is a little water on top, I just pour it off to keep the sauce thick.
The roasted tomatoes, peppers (I use super cayennes, but go by your own family's taste for heat, bells would be fine if that's what you like), roasted garlic (I don't bother to peel them) -- the sauce is made when you thaw without having to stand over a pot of tomatoes on the burner.
Oh, the liquid that drips off the seeds? I also freeze that and use in soup.
