Cream butter, gradually adding sugar. Sift flour and baking powder. Beat egg, egg yolks and almond flavoring. Add lemon rind. Add eggs alternately with the flour ot the cream mixture. Mix well. Place this dough in the fridge in an airtight container overnight.
Make the pudding according to directions on package. Stir in almond flavoring and then cool.
Roll out about 5/8 of the gateau dough the same as you would a thick pie crust. Press it into an 8 inch pie pan and trim the edges. Pour the cooled pudding into the bottom crust. Make a thick top crust with the balance of the gateau dough. Trim edges and then seal them with the egg wash (the mixed egg and water) The pudding expands during the baking process and it will spill over if the edges are not well sealed. Brush on egg wash over the top of the gateau as well. Decorate the top of the gateau by carefully making diamond designs with a fork.
Bake gateau in a preheated 350 degree oven for about 40 min or until it becomes a golden brown. Cool.