Step 1

Preheat oven to 400 degrees F (200 degrees C).

Step 2

Line two 9-inch pie plates with crusts. Cover crusts with a double layer of aluminum foil and a layer of pie weights or dried beans.

Step 3

Bake in the preheated oven until edge of crust is golden, about 10 minutes. Carefully remove the foil and weights; continue baking until the crust sets, about 5 minutes more. Let crusts cool briefly. Reduce oven temperature to 350 degrees F (175 degrees C).

Step 4

Sprinkle cheese, spinach, and onion evenly onto the crusts. Whisk eggs, milk, salt, and pepper together and divide evenly between the crusts.

Step 5

Bake in the center of the preheated oven until golden brown and firm in the centers, about 45 minutes.