You start by coring the tomatoes, removing the stem area and roughly chopping them. Move them to a large pot preferably with a wide base to it. This will help speed up the cooking time because the heat can reach the tomatoes more easily. Add 1/4 cup of olive oil and turn the stove top on high. Bring to a boil.
As soon as you reach a consistent boil, reduce the heat until it is just simmering. About medium heat. Be careful to not scorch the tomatoes to the bottom of the pan. Scraping the bottom with a silicone spatula can help prevent this. Cook for about 30 minutes or until you reach the consistency of tomato sauce.
Start heating your oven to 300°f while cooking your sauce.
Move the tomato sauce to a fine mesh sieve or very fine colander. press them through to remove the seeds and skins. (You may use a food mill for a much easier job but we don’t all have those.)
Oil a large dutch oven or rimmed baking sheet tray. 13x8” half sheet tray or a few smaller trays work fine.
Add the pressed out tomatoes and make sure that it is leveled. Bake until the liquid turns to a thick and rich texture. This will take 3 hours. During the bake, you will need to use a silicone spatula to tend to the edges as they tend to burn more quickly. Simply scrape the edges every so often and move to the center and move some from the center to the edges. This will allow it to cook evenly and create one rich flavor.
Reduce the heat to 200°f and continue baking slowly for as long as possible. This can even cook overnight at this nice low temperature. We are now just dehydrating and reducing the tomatoes down to a paste to concentrate all of that flavor. You should check it once in a while during this process but it does not need nearly as much attention as before.
Once finished, you will be left with a very thick, rich, and tomatoey flavored paste. Take a taste once it is cooled. I dare ya. It is unreal.
You can now freeze it in vacuum seal bags or small freezer bags. Or jar/can it. Be sure to follow a good canning manual so that you do not introduce bacteria.