For the crust:
1) Sift together flour, salt, sugar, and baking powder into a bowl. Cut vegetable fat into flour mixture with a pastry cutter or fork until mixture resembles cornmeal. Stir in 60ml of the cold water, then add remaining water and mix until combined. Cover dough and allow it to rest in refrigerator for 30 minutes.
2) Divide dough in half. Place on lightly floured board and pat out. Using a rolling pin, roll out 1 piece of dough to the size of a 20-cm pie tin. Put crust in pan and trim off excess dough around the edge. Roll out second ball of dough for pie crust top.
For the filling:
Preheat oven to 220C/Gas 7.
1) Mix sugar, tapioca, zest, cinnamon, nutmeg, and sultanas in a large bowl. Lay tomato slices in pie crust. Sprinkle mixture over tomatoes. (Overlapping will occur but tomatoes will shrink in size when baked.)
2) Gently lay top pie crust over filling, tucking in the extra crust around the edges. Pinch dough with fingers or butter knife to seal edges. Using a knife, make 4 to 6 slits in top of crust to allow steam to escape. Brush top with egg white and sprinkle with a little sugar to give your crust a shine.
3) Place pie in the preheated oven and bake for 25 minutes. Reduce temperature to 180C/Gas 4 and continue to bake for 20 more minutes. Cool on wire rack.
*Cook's Note: If your pie looks ready to "spew out," open oven door for about 2 minutes.