For the pastry
Mix well all the ingredients and knead to make a consistent and homogeneous dough. Line a pie tin with the dough and bake in the oven until golden.
For the filling
Bring water to the boil and add some butter. Allow to cool. Combine some water with the different flours and sugar. Bind the mixture with the cooled water plus butter and the
lemon juice and cook. When still warm, add the egg yolk and stir well. Pour the mixture into the pastry and place into the oven. Serve cool.