Preheat the oven to 400°F. Move a rack to the lowest position in the oven.

Poke the bottom of the frozen pie shell several times with a fork, and transfer to a baking sheet.

Bake the pie shell on bottom rack of oven until the bottom is slightly puffed, 12-14 minutes, or according to package directions. When done, remove from oven and set aside.

Reduce the oven temperature to 350°F.

Set a large skillet over medium-high heat and add the olive oil. Once the oil is shimmering, add the spinach leaves. Cook, stirring frequently, until the spinach is fully wilted, about 1 minute. Remove the skillet from the heat and set aside.

In a large mixing bowl, whisk together the eggs, milk, heavy cream, salt, and black pepper, until smooth.

Add the spinach and cheeses to the egg and milk mixture. Fold with a rubber spatula until evenly distributed.

Pour the egg, spinach, and cheese mixture into the pie shell. Cover the edges of the pie shell with pie guards or strips of aluminum foil to avoid burning or over-browning the crust.

Bake the quiche on bottom rack of oven until the top is firm and golden brown, 45-55 minutes.

Check to see that quiche is done. Remove from oven or add time as needed.

Allow to cool for at least 30 minutes at room temperature before slicing and serving. Leftover quiche may be stored covered in the refrigerator for up to 3 days.