Summer Squash, Spinach, and Leek Frittata

Procedure

1. Split the leeks in half lengthwise, and then slice them crosswise into thin slices.
2. Trim and slice the squash.
3. Heat the butter in a sauté pan over moderate heat.
4. Add the leeks and sauté until wilted.
5. Add the squash and sauté until just tender.
6. Remove from the pan and cool.
7. Blanch the spinach