Slice the squash in half lengthwise. Peel off the rind, and scoop out the seeds and pulp. Reserve the pulp for the soup or another dish.
Add the squash rind, squash seeds, leeks, fennel, and sage sprigs to a stockpot. Add the water, and bring to a boil over high heat. Reduce the heat to low and simmer, uncovered, for 45 to 60 minutes.
Strain the broth, and discard the solids. The broth may be refrigerated in a covered container for up to 3 days or frozen for up to 1 month.
The broth may be refrigerated in a covered container for up to 3 days.
The broth may be frozen for up to 1 month.