Croatian cheese pie (pita od sira)

It seems a trifle complicated, this recipe. Trust me, it’s worth the trouble. All my friends like this melt-in-your-mouth cake.

In a big bowl, sift flour, baking powder, add sugar, butter, lemon peel and mix until the consistency of couscous grains. Add beaten egg yolks and sour cream, if desired. Mix until the dough is uniform, soft and a little sticky. Wrap in plastic foil and put in the fridge (or freezer-30 minutes!) for an hour. In the meantime prepare the filling. Beat egg whites until stiff, add sugar a little at the time and beat untill glossy. In another bowl mix soft butter with 500 g of white cheese ( fromage blanc). Gently fold in the egg whites, add lemon juice. On lightly floured cloth roll out half of the pastry to fit a rectangular pan. Bake in preheated 180°C oven for 5-8 minutes until the pastry turns white. Take it out and pour the filling over it. Top with the remainiing half of the rolled pastry. Cut vents with a knife. Return to the oven and bake until crust is golden, 20 to 30 minutes more. Cool on wire rack and dust lightly with powdered sugar.