This stock owes its depth to last summer's crop of potatoes and leeks, simmered into a thick broth. If you don't have leeks, a fat head of garlic, unpeeled and coarsely chopped, makes a fine substitute.
Combine all ingredients in a heavy-bottomed stock pot, along with 8 cups water or more as needed to cover the vegetables. Bring to a boil, reduce heat, cover and simmer for 30 minutes. Pass broth through a food mill or a sieve, pressing on vegetables to extract as much juice as possible.
Nutrition Note: After straining and skimming, broth has negligible calories and nutrients.