Preheat the oven to 350°F (175°C). In a mixing bowl, combine the flour, softened butter, powdered sugar, and salt. Cut or rub together until the mixture resembles coarse crumbs.

Add the egg yolk and a splash of water if needed, then press the dough evenly into a tart pan, trimming the edges and docking the base lightly.

Bake for 15–20 minutes until the edges and base are light golden, then remove and cool completely on a wire rack.

In a saucepan, whisk together the sugar, cornstarch, and 1 cup water until smooth. Place the pan over medium heat and stir constantly until the mixture thickens and becomes glossy.

In a separate bowl, whisk together the 3 large eggs, 2 egg yolks, fresh lemon juice, and lemon zest.

Pour a few spoonfuls of the hot sugar-cornstarch liquid into the eggs while whisking to temper them, then slowly whisk the warmed egg-lemon mixture back into the saucepan.

Return to medium-low heat and cook, stirring constantly for about 2 minutes more until the curd is thick and glossy.

Remove the pan from heat and stir in the 4 tablespoons of unsalted butter a little at a time until fully melted and incorporated.

Pour the finished lemon curd into the cooled tart crust, smoothing the top with a spatula. Chill in the refrigerator for at least 2 hours until set.

Before serving, scatter fresh berries on top and dust lightly with powdered sugar.

For clean slices, run a sharp knife under hot water, dry it, and slice in a single smooth stroke.