Partially bake your pre-made pie crust according to the package instructions. For instance, if it says to bake at 350 degrees F for 20 minutes, then bake it at 350F for 10 minutes. Remove from the oven and set aside.

Adjust oven temperature. The quiche will cook at 325F so adjust accordingly once the crust has finished baking.

Cook the veggies. While your crust is baking, warm the olive oil in a large pan over medium-high heat. Add the diced onion and sauté until it begins to soften, about 2 minutes. Add the mushrooms and sauté 2 minutes before adding the spinach. Season with salt and pepper to taste and cook until the mushrooms are tender and the spinach has wilted. Remove from heat and set aside to cool.

Make the filling. In a large bowl whisk the eggs, half and half, milk, ½ teaspoon salt, ½ teaspoon paper and nutmeg. Stir in the gruyere, ½ cup of the mozzarella and the mushroom mixture.

Assemble the quiche. Pour this filling into the crust and sprinkle the remaining ½ cup mozzarella and 2 tablespoons Parmesan over the top.

Bake. Your quiche will bake until puffed, golden brown, and just set in center, about 45 minutes.

Cool 30 minutes. Then cut into wedges and serve.