Preheat your oven to 375°F (190°C). Lay the pie crust into a 9-inch pie dish and prick the bottom several times with a fork.

Line the crust with parchment paper and fill with pie weights or dried beans. Blind bake for 10 minutes, then remove weights and paper and bake for another 5 minutes to ensure a crisp bottom.

While the crust bakes, melt the butter in a skillet over medium heat. Add the minced shallot and cook for 2 minutes until softened.

Add the sliced mushrooms and fresh thyme to the skillet. Sauté for 6-8 minutes until the mushrooms are golden brown and any liquid has evaporated. Remove from heat.

In a mixing bowl, whisk together the eggs, heavy cream, milk, salt, black pepper, and nutmeg until fully combined.

Scatter the cooked mushroom mixture and half of the grated Gruyère cheese evenly across the bottom of the pre-baked crust.

Pour the egg custard mixture carefully over the fillings, then top with the remaining cheese.

Bake for 35 to 40 minutes, until the center is set and the top is golden brown.

Allow the quiche to cool on a wire rack for at least 15 minutes before slicing to let the custard firm up.