Vegetable stock is a healthy and delicious and be used as the base for many dishes, such as cooking whole grains or making a variety of soups.
To prepare your mise en place, peel the celery root, kabocha squash, carrots and onions. Cut everything into approximately 1" -inch cubes.
Clean the leeks and slice into 1" -inch pieces. Cut the heads of garlic in half horizontally.
To roast the vegetables, preheat your oven to 400º degrees Fahrenheit (205º C). Line a large baking tray with parchment or aluminum foil.
In a large bowl, toss the celery root, kabocha squash, carrots and onions together with the oil and coat. Rub each half of garlic with oil and lay everything onto the baking sheet.
Roast the vegetables until they are nice and caramelized, tossing half way through to brown all sides. To prevent the garlic from developing bitter flavors, remove it from the tray once golden and just roasted.
During the last 10 to 15 minutes or so of roasting, add the leeks, being careful not to burn them.
You can build more flavor and body into the vegetable stock by adding a variety of ingredients (see notes below).
Core the tomatoes and roughly chop. Slice the corn on the cob into 1" -inch slices or measure out the corn.
Measure out the mushrooms and set aside.
Once the vegetables are roasted, heat a large, heavy-bottomed pot over medium-high heat.
Once hot, add the oil, followed by the vegetables. Add the tomato paste, if using, and cook for a few minutes to bring out the flavor.
Add the mushrooms, corn and chopped tomatoes. Add cold water just to cover (plus about 2" -inches) and slowly bring to a gentle simmer.
While the stock is coming to a simmer, gather the bouquet garni.
Add the bouquet garni to the stock, along with a bit of salt, if desired (about 1/4 tsp per liter/quart of water). Let the stock simmer gently for approximately 1 1/2 hours.
Once the stock has simmered, strain, cool and defat, if necessary.
Use the stock in a variety of recipes or freeze it and store it for future use.
Vegetable stock or broth can be made with nearly any combination of vegetables. Just keep in mind that strong-flavored vegetables, such as cabbage, eggplant, turnips or peppers can dominate the flavor, so these should typically be omitted.
Ingredients such as corn, or even corn cobs, add a buttery mouth-feel to the stock (basically what gelatin offers to meat stocks). Celery root and parsnips offer some bite; tomatoes and dried mushrooms (i.e., chanterelle, porcini, or shiitake) can offer great depth of flavor.
A wide variety of herbs and spices, such as tarragon or fennel seeds, can add more complex notes. Even experimenting with items such as sea weeds, dulse, or certain legumes such as chick peas and lentils can give surprisingly satisfying results.
Vegetables stocks, due to the lack of animal protein and fat, tend to last a bit longer in the refrigerator. An excellent vegetable stock can easily substitute chicken stock in almost all dishes, so don’t think of them as second rate at all.