Combine flour and sugar in a large mixing bowl, then cut in the butter until the mixture resembles coarse crumbs.

Gradually add an egg yolk and a splash of cold water, mixing until a dough forms. Shape it into a disk, wrap in plastic wrap, and chill in the refrigerator for at least 30 minutes.

Preheat your oven to 375°F (190°C). Roll out the chilled pâte sucrée on a lightly floured surface to about ¼ inch thick.

Transfer the dough to a tart pan, pressing it into the edges. Place parchment paper on top and fill with pie weights.

Bake for 15 minutes, remove the weights, and return to the oven for another 5-6 minutes until golden brown. Let it cool completely.

In a medium saucepan over low to medium heat, whisk together granulated sugar, lemon juice, and eggs. Whisk vigorously until the mixture thickens and reaches 180°F (82°C), about 10 minutes.

Keep an eye on the mixture to prevent it from curdling; it should coat the back of a spoon.

Remove the filling from heat. Let it cool slightly, then gradually whisk in butter until fully melted and emulsified.

The mixture should be smooth and glossy.

Pour the lemon filling into the cooled tart shell, smoothing the top with a spatula.

Allow it to sit at room temperature for a few minutes before transferring it to the refrigerator. Chill for at least 4 hours.

Before serving, garnish with fresh berries brushed with warmed apricot or orange jam.

Slice into wedges and serve chilled.