Place a medium sized frying pan over medium-low heat. Add olive oil and swirl in the pan. Add the onions and cook, stirring often, until they’re brown and caramelized, about 15-20 minutes. Remove from heat to cool.

Preheat oven to 350°F. Spray a quiche pan (or 9-inch pie pan or square baking dish) with nonstick cooking spray.

Remove spinach from box and place in several layers of paper towels or a clean kitchen towel. Squeeze out all the water from the spinach. Remove towel.

Whisk eggs and milk until frothy. Stir in the spinach, onions, cheese, salt, and pepper.

Pour into prepared pan. Bake 35-45 minutes, or until it’s browned and no longer jiggly. (If you have an instant thermometer, it should read about 170°F internal temperature when it’s done.)

Cool slightly then serve. Store leftovers in refrigerator. Best eaten the day it’s made.