3 cups onions, peeled and roughly chopped
1 cup celery (no leaves), roughly chopped
1 cup carrots, roughly chopped
½ cup leeks, chopped
1 cup mushrooms, quartered
2 tomatoes, quartered
4 cloves garlic, halved
½ cup fennel, chopped (optional)
1 ½ teaspoon dried parsley
1 ½ teaspoon dried thyme
1 ½ teaspoon dried oregano
1 tablespoon black peppercorns
One 4 x 4 inch piece of cheesecloth
6 inches butcher twine
2 quarts cold water
For thickened vegetable stock:
2 cups vegetable stock, plus 4 tablespoons
4 tablespoons cornstarch
Heat a large stockpot over medium-high heat and add the vegetables. Stir occasionally for 3 to 5 minutes to prevent scorching. Tie spices and herbs inside a cheesecloth with butcher twine. Add to pot. Cover contents with cold water and bring to a boil. Reduce heat to medium-low and simmer for 2 hours.
Strain stock and use immediately or cool in an ice bath and then refrigerate or freeze for future use.
To make thickened vegetable stock:
In a 6 quart saucepan, bring 2 cups of vegetable stock to a rolling boil. Combine 4 tablespoons of cold stock with the cornstarch to make a slurry (a thick mixture). Add the slurry to the boiling stock while whipping constantly until the mixture is smooth and has a sauce-like consistency.
Cool completely in an ice bath. Cover and refrigerate for later use. Thickened stock will keep up to one week. Stir well before each use.