In a large mixing bowl, combine all-purpose flour and sea salt. Cut in very cold butter until the mixture resembles coarse crumbs, about 5 minutes.

Gradually incorporate ice water, adding just enough for the dough to come together. Shape the dough into a disc, wrap it in plastic, and refrigerate for 1 hour.

Preheat your oven to 400°F (200°C) while the dough chills.

Roll out the chilled dough into a rough 12-inch circle. Transfer the dough onto a prepared baking sheet.

Spread a thick layer of mascarpone cheese over the dough, leaving a 1-inch border around the edges. Arrange sliced heirloom tomatoes on top.

Sprinkle with sumac, sea salt, and pepper. Fold the edges of the dough over the filling to create pleats.

Bake for 30-35 minutes until the crust is golden brown and the filling is bubbling.

Allow to cool slightly before serving warm or at room temperature.