In a large mixing bowl, sift together pastry flour, powdered sugar, baking powder, and a pinch of salt. Incorporate very cold, cubed unsalted butter using your fingertips until resembling sandy crumbs. Add one egg to bind, mixing until a dough forms. Wrap in plastic and chill in the freezer for 20 minutes.

Roll out the dough between two silicone mats to about 1/8-inch thickness. Transfer to a 9-inch pie dish, trim excess. Chill for another 15 minutes, then blind bake at 350°F for 40 minutes until golden brown.

While the crust cools, whip drained ricotta cheese until smooth. Gradually add granulated sugar, mixing until combined. Add room-temperature egg yolks and heavy cream, mixing continuously. Fold in lemon zest.

Pour filling into the pre-baked crust, smoothing the top. Cover edges with foil, and bake for an additional 45 minutes at 350°F. Edges should be set and center slightly wobbly.

Remove from oven, cool at room temperature for about 3 hours to fully set. Prepare whipped topping during this time.

Whip cold mascarpone cheese with heavy cream and powdered sugar until fluffy. Pipe generously onto cooled pie.