The first tomato paste I ever tried to make was a romantic pursuit involving crushing the tomatoes and laying them out in the late summer sun to gently dry. While it didn’t turn out as I hoped, the flies loved it. With the second attempt I tried cooking the tomatoes down on the stove top then roasting them in the oven on low heat for what seemed like an eternity. For the perfect combo of quick and romance of fermentation there is this wonderful method.
Start by cutting up the tomatoes and placing them into a container to ferment in. Nothing else needs added, just leave at room temperature with a secure covering- cloth or otherwise, for 3-7 days.
The fermentation will separate the water from the solids to the point that you can hand scoop out the tomato peices leaving behind a big pool of tomato water. Run the tomato bits through a food mill to get the seeds and skins out.
Then strain the solids to the consistency of paste you desire. When it’s done you can mix in some salt or coat the surface with oil after its packed in a jar to help a little with preserving- or leave it as is. Keep in mind that it’s an alive and active ferment so if you pop on a lid it will produce some gas.