How to Make It
In a dry 6-qt. pot, toast coriander and caraway seeds over medium-high heat until fragrant and a shade darker, 3 to 4 minutes. Pour into a small bowl and set aside.
Swirl in 1 tbsp. oil, reduce heat to medium, and add onion. Cook, covered, until softened and beginning to brown, stirring occasionally, about 10 minutes. Add leeks, toasted spices, peppercorns, bay leaves, and 9 cups water. Bring to a simmer over medium-high heat, covered.
Add cheese rinds and kelp, bring back to a simmer, and adjust heat to maintain a gentle simmer, uncovered, 1 hour, stirring now and then. Remove from heat and let stand 1 hour, covered. Strain through a fine-mesh sieve.
*Find kombu at well-stocked grocery stores and Asian markets. Hoard your leftover cheese rinds in the freezer until you have enough to make a batch (or even a half-batch) of stock.
Make ahead: Up to 1 week chilled; up to 3 months frozen.
Pilgrimme restaurant, Galiano Island in British Columbia