Preheat the oven to 400º.

Dough:

Combine the flour and salt in a medium-sized bowl. Add the butter to the mixture, using your fingers to incorporate the butter into the flour/salt mixture. Add the mascarpone, lemon juice and ice water to the bowl. Knead together until the mixture forms a soft dough. If the dough seems too dry, add more ice water. If the dough seems too wet, add more flour. Wrap dough ball in plastic wrap and refrigerate until ready to use. You’ll want to keep the dough chilled for 30 minutes to an hour before assembling the tart.

In a separate bowl combine the nectarines, cornstarch and lemon juice in a bowl. The cornstarch will thicken the nectarines. Allow the nectarines to sit for 10-20 minutes to thicken.

In a separate medium-size bowl, combine the lemon zest and the full cup of mascarpone.

To assemble, roll the dough on a parchment-lined baking sheet. Roll dough into a large 16″ circle. If the dough softens too much, place the baking sheet in the freezer to chill again. Layer on the mascarpone/lemon zest in the center, keeping 1/2-1 inch of dough free of the mixture around the edges. Add the nectarines on top of that layer. Gently fold the edges up around the edges of the filling.

Beat an egg yolk in a small dish, using a pastry brush apply the egg yolk to the crust. Top the egg yolked crust with a sprinkle of white sugar.

Bake in the oven for 40 minutes until the crust is golden brown.