Take a pan, boil milk along sugar, lemon zest and butter. Then let it cool down a bit, add lightly beaten egg yolks and mix well. Take a greased oven dish, arrange bread slices and pour milk mixture, bake on 180 degree preheated oven for 15 minutes. Then take it out and spread jam all over, then spread egg whites and bake again on 200 degree for 5 minutes or until you can see light golden colour on top. Serve hot.