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1. For the dough, pulse the flour, butter, and ¼ tsp salt in a food processor until the mixture resembles coarse bread crumbs. Add the water and pulse until the dough comes together, adding more water if needed. Shape into a thick disk and wrap in plastic wrap. Refrigerate for 30 minutes. Roll out into a round about 1/8 in (3mm) thick. Use the dough to line an 8in (20cm) fluted tart pan with a removable bottom. Chill for 30 minutes.

2. Preheat the oven to 400°F (200°C). Prick the bottom of the pastry shell. Line it with parchment paper and fill with baking beans. Bake about 15 minutes, until the dough looks set. Lift off the parchment paper and beans. Bake for 10 minutes more, until beginning to brown. Transfer to a wire rack.

3. Slice the squash into thick slices and spread on a baking sheet. Toss with 1 tbsp oil. Bake for 30 minutes, or until tender. Meanwhile, cook the spinach and 2 tbsp olive oil in a covered saucepan for about 4 minutes, until wilted. Drain and let cool. Whisk the eggs, egg yolk, cream, Parmesan, and nutmeg together and season to taste with salt and pepper.

4. Squeeze the spinach dry. Spread it in the pastry shell, and top with the squash and Gorgonzola. Pour in the custard. Bake for about 30 minutes, or until the custard is set. Let cool for 10 minutes. Remove the sides of the pan and serve hot.