Make the pastry first: sift the flour and salt into a mixing bowl and cut in the butter until it resembles coarse crumbs. Mix together the water, egg and lemon juice and blend gently into the flour mixture. Wrap the dough in plastic wrap and chill 4 hours or overnight.
Make the filling: in a saucepan, mix together the dry ingredients. Add the 1/2 cup water and mix well. Bring to a simmer and cook 5 minutes, stirring. Mix in the apples and simmer 10 more minutes.
Preheat the oven to 230 degrees C and butter a baking tin.
Divide the dough in half with one half a little larger. Roll out the larger half into a rectangle to fit the baking tin and up the sides. Fill with the apple mixture. Roll out the other piece of dough and lay it over the apples. Seal the edges of the dough and cut a few steam vents.
Bake 20 minutes. Reduce heat to 180 degrees C and bake 30 more minutes. Let cool before cutting into slices.