Sift the flour, baking powder and sugar together in a bowl. Dice the cold butter and rub in the flour until the mixtures resembles coarse bread crumbs. Add the egg, lemon zest and cold water and knead until the dough comes together. Wrap the dough in plastic wrap and place in the refrigerator 30 minutes before rolling out.
Grease a spring release tin and cover the bottom with baking paper. Roll out the pastry and cover the bottom and sides of the tin. Cover and refrigerate for 20 minutes to chill the butter. With the tines of a fork, prick the bottom of the dough (this will prevent the dough from puffing up as it bakes).
Preheat the oven to 175 °C. Line the pastry with baking paper, weigh down with dry filling and blind bake for 15 min or until the dough is dry and light brown. Remove paper and filling, return to the oven for 5 min to allow the dough to dry out. Remove from the oven but leave it switched on.
Filling
Peel and dice the rhubarb and mix them with the sugar, cinnamon, ground ginger, raisins, apricots and half of the custard powder.
Spread the rest of the custard powder on the bottom of the prebaked pastry to soak up any escaping liquid during baking. Place the rhubarb filling on top. Press lightly to compress.
Brush the edges of the pie with the egg yolk, sprinkle the flaked almonds on top and bake the pie at 175 °C for 45 min or until done and golden brown. Place the rhubarb pie in the tin on a wire rack to cool.
Brush the top with the apricot jam mixed with hot water to give it a glossy finish and to prevent it from drying out. Let the pie cool completely before portioning.
Stuff to know
This quantity will yield a pie of 24 cm Ø. Use a filling of both apples and rhubarb. Let the dough chill in the fridge before you fill and bake the pie so it won’t shrink in the oven. Prebaking the pastry will prevent it getting soggy.
Recipe by Jeroen Valkenier Recipes at https://jpvalkenier.com/rhubarb-tart/