Soup – How to get a thicker soup from watery tomatoes

None of the answers so far mention collagen -- specifically, using a stock made from roasted and cracked poultry bones.

You don't have to roast the bones, but you do need to crack them -- use a large, heavy knife or cleaver (not a chinese vegetable cleaver, you'll screw up the edge) to chop the bones up into about 2" to 3" pieces (5 to 7cm). Put them in cold water, and slowly bring it up to a simmer, and just leave it simmering for a few hours. You can add vegetables, too, but you'll want to pitch them, as they'll have been overcooked by the time the simmering's done.

Then strain everything, and use that as the base of your soup.

If your refrigerate stock that has enough collagen in it, it'll set up like jello, and hold its own shape. Starches can work, but they're not ideal for soup -- flour (unless cooked as a roux) leaves a raw flour taste and cloudy soup; tapioca leaves little granules in there; corn starch will break down if you cook it too long.

There's a few types of salsa -- salsa fresca (aka pico de gallo, aka salsa cruda), which is "fresh salsa" and uncooked, and if made fresh, it shouldn't be too watery (unless you add to much liquid, eg, lime juice), but letting the vegetables sit after salting will start to draw out extra liquid and could become watery.

For truly thick salsa, you have to treat it like a jam, and cook it to release the pectin in the tomato. (or I guess you could use some other thickeners ... I've never tried. tomato paste, maybe?) You don't necessarily have to cook the other ingredients, too, but I personally like roasting the peppers and onions to sweeten then up and remove some of the extra liquid. (halve the peppers and seed them, lay them on a tray cut side up with the onion cut into wedges, roast 'til they're softened, then dump into a food processor and either pulse or liquify it, depending on how chunky you like it. And the skin falls off the peppers, so I leave 'em out).

You can do the same roasting with the tomatoes, and it'll be thicker from the food processor, but you won't get the same cling without letting them cook slowly in liquid to develop the pectin. If you roast the tomatoes, I like to use plum tomatoes, as they have more "meat" to the gel around the seeds, and take out the gel and seeds.