Previously I showed you how to make instant miso soup balls  to which you just add boiling water to make a hot cup or bowl of soup. But even I don’t want miso soup all the time. Instant soup mixes are an option, but they are usually rather salty, and don’t contain a lot in terms of nutrients. So I set about experimenting with making my own instant soup concentrate. After some trial and error, here’s a formula for a Mediterranean tasting vegetable soup concentrate that works pretty well. It does take some mostly unattended time to cook down, so it’s a good project to do over the weekend to stock up for upcoming bento lunches.
Chop up all of the vegetables fairly finely but not too finely. You can do this in a food processor, or just chop by hand.
Heat up a heavy bottomed pot with the olive oil. Add all the vegetables, and sauté until limp.
Add the can of tomatoes and tomato paste, plus a little water (rinse out the can and pour that water in). Add the herbs, salt and stock cube. Bring to a boil, then simmer over a low heat until the mixture has reduced to about 1/4th, stirring up from the bottom occasionally to prevent it from burning. The moisture should be just about gone, and it should look like a very thick vegetable-studded sauce. The cooking down process takes about half an hour or more, so you’ll want to do this when you can be around the kitchen to check up on its progress.
Let the mixture cool, and take out the bay leaf. If you taste it at this point it should be quite salty - too salty to eat on its own, since you will be diluting it with hot water.
Wrap up 2 tablespoon portions in plastic wrap, put the packets in a zip bag, and freeze. This amount makes about 10 portions.
When you want to bring one along, just pack a frozen packet.
By lunchtime, the packet will have defrosted.
Squeeze out the contents of the packet into a mug or bowl.
Add boiling water. Mmm, piping hot veggie soup.
Adding some precooked pasta and beans will turn this into a minestrone!
The plastic wrap packet does tend to leak a bit once the mixture has defrosted, so be sure not to carry it on its own. Yu may want to put it inside a divider cup in your bento if you don’t want the surrounding food to be tomato-stained.
There’s a lot of salt in this, because it is a concentrate. If you want to regulate the salt more, omit it from the concentrate and add salt to taste when you mix up your cup of soup. Sprinkling in some dried herbs when mixing will help with that too. (It makes you realize how salty instant soup mixes are…)
I think you could make a lot of variations of this basic method of cooking a concentrated sauce or paste to use as a soup base. I’ll post them if I come up with others, and let us know in the comments if you come up with your own ideas!