This recipe from Cook's Illustrated magazine is genius. Most vegetable stock recipes call for simmering a lot of whole vegetables, sometimes roasted in advance, then straining them, to make a relatively small amount of stock. This recipe uses small amounts of whole vegetables, herbs and aromatics to make a concentrate - and no cooking at all! Keep it in your freezer and you've literally got it made!
Since this recipe is for a concentrate, and because it’s from Cook’s Illustrated magazine, the ingredients and amounts are very specific. You can probably vary this to some degree, but try it as-is first. I once subbed onion powder for the dried onions and it wasn’t as good - but using other herbs, adding dried mushrooms, subbing parsnip for carrots or for celery root, would probably work out fine.
Vegetable Stock Concentrate
Makes enough for 7 quarts of stock!
2 leeks, white and light green parts chopped and washed (2 ½ cups or 5 oz.)
2 carrots, cut into ½” pieces (2/3 cup or 3 oz.)
½ small celery root, peeled and cut into pieces (¾ cup or 3 oz.)
½ cup parsley leaves and thin stems
3 tbs. dried minced onions
2 tbs. kosher salt (not Morton's) or 4 tsp. regular table salt
1 ½ tbs tomato paste
3 tbs. soy sauce
Using a food processor or blender, add leeks, carrots, celery root, parsley, onions and salt and make a smooth paste, scraping down the sides of the container as necessary. Add tomato paste and mix. Add soy sauce and mix.
Transfer to an airtight container and keep in the freezer. The concentrate won’t get completely hard because of the salt. Scrape out one tablespoon per cup of boiling water to make a delicious stock.