Combine flour and granulated sugar, then cut in softened butter until it resembles coarse crumbs. Gradually add cold water, mixing until the dough forms. Shape into a disk, wrap in plastic, and chill in the refrigerator for at least 30 minutes.

Preheat your oven to 375°F (190°C). Roll out the chilled dough and fit into a tart pan. Line with parchment and fill with pie weights. Bake for 10 minutes, remove weights, then bake for another 5 minutes until golden brown.

In a medium saucepan, whisk granulated sugar and lemon juice over low to medium heat until the mixture thickens and reaches 180°F (82°C), approximately 5-7 minutes. Remove from heat; whisk in unsalted butter until smooth.

Let the lemon mixture cool for about 5 minutes. Add room-temperature eggs one at a time, whisking vigorously until incorporated.

Pour the lemon filling into the cooled tart shell, spreading evenly. Place in the refrigerator and chill for at least 3-4 hours until set.

Top with fresh berries and brush a light layer of warmed jam for glaze. Slice and serve.