Put the tomatoes in a bowl. Refine with 2 pinches of salt and 2 pinches of stevia. We add about 1 g of ascorbic acid (vitamin C) as an acidulant and to preserve it.
Mix the whole thing together nicely. Using a funnel, pour the ketchup back into the glass and put it in the refrigerator. And the simple, cheap and healthy ketchup is ready.