Sift together pastry flour, powdered sugar, baking powder, and salt in a large mixing bowl. Incorporate cubed unsalted butter by rubbing it in with your fingertips until the mixture resembles coarse sand. Add egg and mix until a dough forms. Knead gently for 1-2 minutes, then wrap in plastic and chill in the fridge for 30 minutes.

Preheat your oven to 170°C (338°F). Roll out the dough on a floured surface to fit a 9-inch pie dish. Place the rolled dough into the dish, trim the edges, and freeze for another 30 minutes. Once set, line the crust with parchment paper, fill with pie weights, and bake for about 40 minutes, or until golden brown. Remove from oven and let cool.

Prepare the filling by whipping drained ricotta cheese with granulated sugar until smooth. Gradually add in room-temperature egg yolks and continue to whip until well combined. Stir in heavy cream and corn starch until fully blended, then gently fold in the zest of 2 lemons.

Pour the filling into your blind-baked crust, ensuring it’s evenly distributed. Cover the edges of the crust with foil to avoid over-browning. Bake for another 45 minutes, until the center is slightly wobbly while the sides look set.

Allow the pie to cool at room temperature for at least 3 hours. This resting period helps the filling firm up.

In a mixer, combine mascarpone, cold heavy cream, and powdered sugar. Whip together until fluffy, mixing in the zest of 1 lemon. Pipe or spread this topping generously over the cooled pie before slicing and serving.