Rinse the tomatoes well, remove the stems, and cut into chunks.

Fill a blender jar with the tomato chunks and blend until the tomatoes have all reduced into a sauce.

I don't filter the skin or seeds...I process the whole tomato. However....if you don't want to do it my way....here's how to rid the skin and seeds: Place a stainless steel strainer over your slow cooker pot.... and pour the tomato sauce into the strainer. Use a stainless steel spoon or a spatula to press the tomato sauce through the strainer into the pot below.

Heat the sauce with the low heat setting ..... stirring every once in a while and checking on the consistency. As the water evaporates away, the sauce will continue to thicken. Make sure to leave the lid off the slow cooker or the water won't evaporate away

To give the tomato paste a more caramelized flavor.... and reduce it even further......  bake it on clean olive oiled coated baking pans on low heat in the oven. Scrape the tomato paste from the bottom of the tray with a spatula, stirring it into the rest as you frequently check on the consistency.

Freeze it! No canning.