In a medium bowl whisk together 1.25 cups all-purpose flour, 2 tsp granulated sugar and 1 tsp fine sea salt. Add 0.5 cup cold cubed unsalted butter. Using a pastry cutter or your fingertips, cut the butter into the flour until mixture resembles coarse crumbs with some pea-sized bits remaining (about 6–8 passes).

Bring dough together

Sprinkle 3 tablespoons cold water over the flour-butter mixture and mix gently with a fork until dough starts to clump. If needed, add up to 1 more tablespoon water, 1 tsp at a time, just until it comes together. Do not overwork.

Chill and roll

Form dough into a disk, wrap in plastic, and chill in the refrigerator for at least 30 minutes. After chilling, on a lightly floured surface roll the dough to a 11-inch circle about 1/8–1/4 inch thick. Fit into a 9-inch (23 cm) tart or pie pan, trimming and crimping the edges. Chill the lined pan for 15 minutes in the fridge.

Blind-bake

Preheat oven to 375°F (190°C). Line the chilled crust with parchment and fill with pie weights or dried beans. Bake for 15 minutes, then remove weights and parchment and bake another 8–10 minutes until crust is set and lightly golden. If using egg wash, brush beaten egg on the bottom and sides and return to oven 2–3 minutes to set. Let crust cool while preparing the filling.

Yuzu Curd Filling

Mix eggs and sugar

In a medium heatproof bowl whisk together 4 egg yolks, 1 whole egg and 1 cup granulated sugar until smooth and slightly pale, about 1–2 minutes.

Temper with juice

In a small saucepan combine 0.75 cup yuzu juice, 1 tablespoon yuzu zest, 1 teaspoon cornstarch (if using) and 1/4 teaspoon fine sea salt. Warm gently over low heat until just steaming — do not boil. Slowly ladle about 1/3 of the warm yuzu liquid into the egg-sugar mixture while whisking constantly to temper the eggs. Repeat with another 1/3, then pour the tempered egg mixture back into the saucepan with the remaining yuzu liquid, whisking constantly.

Cook curd

Cook the mixture over low-medium heat, stirring constantly with a heatproof spatula or whisk, scraping the bottom, until it thickens and reaches a custard consistency and coats the back of the spatula (about 6–8 minutes). Do not let it boil — if it begins to steam heavily, reduce the heat.

Finish with butter

Remove the pan from heat and immediately whisk in 0.5 cup (8 tablespoons) cold unsalted butter, one tablespoon at a time, until fully incorporated and the curd is smooth and glossy. Stir in extra 1 tablespoon yuzu zest if you like a stronger aroma. Taste and adjust salt or sweetness — add up to 1 tablespoon sugar if needed.

Strain and cool

Pass the curd through a fine-mesh sieve into a clean bowl to remove any cooked egg bits and zest fibers. Cover the surface with plastic wrap to prevent a skin and chill until slightly warm or refrigerated until fully set, about 1–2 hours. If chilled fully, let sit at room temperature 10–15 minutes before filling so it spreads easily.

Fill crust

Pour the yuzu curd into the cooled baked crust and smooth the top with an offset spatula. Return to refrigerator to set for at least 1 hour (longer for firmer slices).

Topping (Optional)

Whip cream

If using topping, chill a mixing bowl and beaters. Whip 0.5 cup heavy cream with 2 tablespoons powdered sugar to soft peaks. Spread or pipe the whipped cream over the chilled yuzu curd, or serve dolloped on each slice.

Garnish

Sprinkle with 1 teaspoon toasted sesame seeds or finely chopped candied yuzu peel for contrast. Serve slices chilled or at cool room temperature.