You wash your tomatoes. It doesn't matter what kind you use. I used big red 'maters, golden, orange, Romas, heirlooms, cherry 'maters, you name it. They all work.
Cut 'em up. I quarter the big ones, and halve the small ones. They cook faster that way. Toss 'em with a little olive oil, then place them on an oiled cookie sheet.
Slice up some onions and toss them in with the tomatoes. Put in some unpeeled garlic cloves too (not peeling them lets them steam instead of dry out, and tends to make them more flavorful and less bitter). Sprinkle it all with a little sea salt, a little oregano and thyme, and whatever other spices float your boat. There's no exact science to it, just throw in whatever sounds good to you, in whatever proportions you like.
Then roast 'em in an oven on 400 degrees for about an hour or so, till they are semi-dried up but still all bubbly. (You choose how dry you want them to get; still a little bubbly is how I like mine.) If you arrange your oven racks properly, you can roast two pans at once.....and trust me, you're going to want to! I did four pans over the weekend and could've done more if I'd had the time.
When they are done, let 'em cool a tad, then use a spatula and scoop them off into a bowl. Taste, and know you've gone to heaven....even if you're not much for cooked tomatoes. Rinse and repeat till you are out of tomatoes or out of storage space.