Preheat your oven to 375°F (190°C).
In a medium-sized skillet, heat the olive oil over medium-high heat.
Add mushrooms and sauté for about 5 minutes, or until they’re tender and slightly golden.
Toss in the chopped spinach, season with salt and pepper, and cook until wilted, approximately 2-3 minutes.
In a separate bowl, whisk together eggs, heavy cream, nutmeg, and a pinch of salt and pepper.
Sprinkle half of the Gouda cheese at the base of the pie crust.
Spread the sautéed spinach and mushroom mixture evenly over the cheese in the pie crust.
Pour the egg and cream mixture over the vegetables.
Sprinkle the remaining Gouda cheese on top.
Bake in the preheated oven for 35-40 minutes, or until the center of the quiche is set and the top is lightly golden.
Remove from the oven and let it sit for about 5 minutes before slicing.