In a bowl, whisk flour and salt. Add chilled butter cubes, then use a pastry cutter until mixture resembles coarse crumbs, like sandy texture.

Drizzle ice water a tablespoon at a time into flour mixture, stirring gently with a fork until dough just holds together.

Shape dough into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

On a lightly floured surface, roll dough to 1/8-inch thickness. Transfer to a 9-inch quiche pan, trim overhang, and crimp edges.

Preheat oven to 375°F, line crust with parchment, and fill with pie weights. Bake for 15 minutes, remove weights, then bake 5 more until edges are golden.

Heat 1 tablespoon olive oil in a skillet over medium-high heat. Add mushrooms and cook until golden brown, about 5–7 minutes.

Add minced garlic and fresh spinach to the skillet, sautéing for 2 minutes until wilted and bright green.

In a bowl, whisk eggs, heavy cream, salt, pepper, and a pinch of nutmeg until smooth and frothy.

Spread mushrooms and spinach evenly in the blind-baked crust. Pour custard over filling until just below rim.

Bake at 375°F for 30–35 minutes or until custard is set and top is light golden. Let cool 10 minutes before slicing.