1. Make a bouquet garni: Cut a piece of kitchen twine about 8 inches long, and tie together leek greens, parsley, fennel, bay leaves, and thyme in a small bundle.

2. In a large saucepan, combine bouquet garni, 9 cups water, and remaining ingredients. Bring to a boil over medium-high heat. Reduce heat to low, and simmer for 35 minutes. Store in an airtight container, refrigerated for up to 3 days and frozen for up to 3 months.

3. Just before using, strain through a fine-mesh sieve.