If you don’t mind a dark broth, add 8 oz [230 g] of cremini mushrooms to this mixture of vegetables for added depth.
MAKES 12 CUPS [2.8 L]
ACTIVE TIME 10 MINUTES
TOTAL TIME 8 TO 9 HOURS
2 medium yellow onions, coarsely chopped, with skins
2 large leeks, white and green parts, halved lengthwise, rinsed, and coarsely chopped
3 large carrots, coarsely chopped
3 large celery stalks, coarsely chopped
1 small fennel bulb, chopped
4 large garlic cloves, coarsely chopped
1 Tbsp tomato paste
8 black peppercorns
6 fresh thyme sprigs
2 bay leaves
1 Tbsp soy sauce
1. In a 7-qt/6.5-L slow cooker, combine the onions, leeks, carrots, celery, fennel, garlic, tomato paste, peppercorns, thyme, and bay leaves. Cover with 12 cups [2.8 L] of cold water. Cover the cooker and cook on low heat for 8 to 9 hours.
2. Strain the broth through a fine-mesh sieve into a large bowl. Add the soy sauce.
Refrigerate, uncovered, until the broth has cooled completely. Store in airtight containers in the refrigerator for up to 4 days, or in the freezer for up to 3 months.
Combine the onions, leeks, carrots, celery, fennel, garlic, tomato paste, peppercorns, thyme, and bay leaves in a large soup pot. Add 12 cups [2.8 L] of cold water and bring to a boil over high heat. Reduce the heat to low, cover, and simmer gently for 1¹/2 hours. Strain and add soy sauce. Refrigerate and store as directed above.