8 tbsp unsalted butter – cut into 0.5-inch cubes and chilled
4 tbsp ice water
1 tbsp unsalted butter
0.5 cups shallot – finely chopped
12 ounces fresh spinach – stems trimmed and washed
4 large eggs
1 cups heavy cream
0.5 cups whole milk
0.75 tsp fine sea salt
0.5 tsp black pepper – freshly ground
0.25 tsp ground nutmeg
4 ounces gruyère cheese – coarsely grated
Instructions
Make the dough: In a bowl, combine the all-purpose flour and 0.5 tsp fine sea salt. Cut in 8 tbsp unsalted butter (cold, cubed) with your fingertips or a pastry cutter until the mixture resembles coarse crumbs with pea-size bits of butter.
Add liquid: Drizzle in 3 to 4 tbsp ice water (up to the full 4 tbsp as needed), tossing just until the dough holds together when pressed. Gather into a disk, wrap, and chill until firm, about 30 minutes.
Cook the vegetables: Melt 1 tbsp unsalted butter in a large skillet over medium heat. Add the finely chopped shallot and cook until translucent, 3–4 minutes. Add the fresh spinach and cook, stirring, until wilted and most moisture evaporates, 2–3 minutes. Transfer to a colander, cool, squeeze very dry, then chop roughly.
Line the pan: On a sheet of parchment, roll the chilled dough into a 12-inch round. Fit into a 9-inch tart pan (with removable bottom) or pie plate, easing into corners. Trim excess, dock the base with a fork, and freeze 15 minutes.
Blind-bake: Heat the oven to 375°F/190°C. Line the crust with parchment and fill with pie weights or dried beans. Bake 15 minutes, then remove parchment and weights and bake until the base looks set and just lightly golden, 5–7 minutes more. Let cool slightly.
Make the custard: In a medium bowl, whisk the large eggs, heavy cream, whole milk, 0.75 tsp fine sea salt, black pepper, and ground nutmeg until smooth and well combined.
Assemble: Scatter the chopped spinach evenly over the baked crust, then sprinkle the gruyère cheese over the spinach. Set the pan on a baking sheet and pour the custard over the filling.
Bake: Return to the oven and bake at 375°F/190°C until the center is just set with a slight wobble and the top is lightly golden, 30–35 minutes. Cool 10–15 minutes before slicing and serving.