In a food processor, combine pastry flour and granulated sugar, pulsing until mixed. Add softened unsalted butter and blend until the mixture resembles coarse crumbs. Incorporate the egg yolk until a dough forms. Shape the dough into a disc, wrap it in plastic, and chill for 30 minutes in the refrigerator to firm up.

Roll out the chilled dough on a lightly floured surface until it's about 1/4-inch thick. Carefully fit the dough into a tart pan, ensuring it covers the edges well. Line the crust with parchment paper and fill it with pie weights. Bake in a preheated oven at 375°F (190°C) for 10-15 minutes, until the edges are lightly golden.

In a medium saucepan over medium heat, whisk together freshly squeezed lemon juice, lemon zest, granulated sugar, eggs, and egg yolks. Cook the mixture, stirring continuously, until it thickens and reaches 180°F (82°C), which should take about 8-10 minutes.

Remove the saucepan from heat and gradually whisk in room-temperature butter, one piece at a time, until fully blended. Let it cool slightly before transferring to the tart shell for an even filling.

Pour the lemon filling into the pre-baked tart shell, smoothing the top with a spatula. Carefully place the tart in the refrigerator and allow it to set for at least 4 hours.

Once set, slice the tart into wedges and serve chilled. Garnish with fresh seasonal berries and a light glaze of warm apricot or orange jam, if desired.