We recently harvested a couple of dozen big yellow tomatoes. We ate what we could, but there were so many that I decided to make sauce out of them, and then cook the sauce down to make golden tomato paste. I didn't season the sauce much. Into the cut-up tomatoes went a teaspoon of salt, a bay leaf, a pinch of hot pepper powder, and about a cup of white wine. I ended up with three liters of sauce.
As the sauce cooked, I mashed the tomato wedges with a big spoon and even a potato-masher to break them down. When the sauce was cooked, I let it cool overnight and then ran it through the food mill (le moulin à légumes) using a fine blade to remove most of the tomato seeds and the tough skins. Then I had a smooth, liquid puree.
I poured the pureed tomato into a big lasagna pan. It made a layer about an inch (2.5 cm) thick. I was afraid that might be too thick to allow for the desired evaporation and thickening, but it worked out fine.
Here are the tomato seeds and skins that were filtered out of the sauce by the food mill. This seedy pulp went into the compost. (Here's a Youtube video that shows how you can use a food mill to make tomato puree.)
I took this photo just because I liked the color of the yellow tomato puree. The lasagna pan went into the upper part of the oven at a temperature of around 150ºC (300ºF) for enough time to bring the sauce to a low simmer. Then I kept turning the temperature down, ending up at about 90ºC (195ºF), and stirring the puree from time to time. After about four hours in the oven, the sauce had thickened into paste.
Cooking the paste in a slow oven gives the puree a chance to thicken by evaporation without scorching on the bottom. There was a little bit of caramelization around the edges of the pan, but that just adds good flavor when you stir it into the paste. As you can see, it really is paste. It looks a lot like pureed pumpkin or butternut squash flesh. However, it's actually tomato paste that I'll put up in sterilized jars today for storage and use over the coming winter.