For the Sweet Tart Dough:

1. Whisk together the flour, salt, and confectioners’ sugar in a medium bowl. Cut in the butter with a pastry cutter until it resembles fine breadcrumbs.
2. Add the egg yolk and water and cut in with the pastry cutter. When the dough starts coming together, knead with your hands just until a smooth dough forms. Do not over-knead.
3. On a lightly floured surface, turn out the dough and press into a flat disc. Tightly wrap in plastic wrap, and chill in the refrigerator for 1 hour.

For the Filling and Assembly:

1. Remove from the refrigerator and divide the dough into 6 equal pieces on a lightly floured surface.
2. Working with one piece at a time, lightly dust the top with flour. With a rolling pin, roll out each piece into a small circle about 1/4 inch thick and about 6 inches in diameter. Use more flour as necessary to prevent sticking.
3. With a pastry brush, spread a thin layer of orange marmalade in the center of the disc, leaving about an inch of space around the edge. Shingle 4-6 slices of oranges on top of the marmalade. Fold up the sides of dough over the filling, forming loose pleats.
4. Immediately transfer to a baking sheet lined with parchment paper or a silicone mat.
5. Repeat with the 5 remaining dough pieces, leaving about an inch of space in between each crostata on the baking sheet.
6. Chill the crostatas in the refrigerator for 30 minutes, or until the dough is cold and firm.
7. Preheat the oven to 400°F while the crostatas are chilling.
8. When ready to bake, remove the baking sheet from the fridge. Whisk the whole egg in a small bowl, and brush the edges of each crostata with a thin layer of the egg wash. Liberally sprinkle the edges and the exposed top of the crostatas with the turbinado sugar.
9. Transfer to the oven, and bake until the crust is a deep golden-brown color, about 35-45 minutes.
10. Remove from the oven, and allow the crostatas to cool on the baking sheet for 15 minutes before transferring to plates and serving with a small dollop of mascarpone cheese on top.