In the bowl, add the solid ingredients: flour, potato starch, sugar and baking powder.
Gradually add the liquid ingredients and the lemon zest, while mixing with the fork.
Knead until you have a homogeneous dough, without lumps. Let it rest in the fridge for 30 minutes, wrapped in some cling film.
Preheat the oven at 180° C/356° F and prepare the cake pan: oil the bottom and flour it, to avoid the pie sticking.
Dust the pastry board with some flour and roll out ⅔ of the dough with the help of the rolling pin. Make sure that you have your final circle big enough to cover the pan (bottom + around 3/4 of the side).
Transfer the dough circle into the cake pan and prick the bottom with the fork.
Fill with the curd and level with the spatula.
Roll out the remaining dough and transfer it over the custard. Seal the edges with the help of the fork.
Garnish with pine nuts and bake for 30-40 minutes at 180° C/356° F, on static mode, in the middle part of the oven.
Take the pie out of the oven and let it cool down completely.
Storage You can store it in Tupperware (or a cake container) for 4-5 days, in a cool and dry place.