For cake, sift flour and baking powder together in a bowl.
In a large bowl cream butter, sugar with an electric beater at medium speed until light and fluffy in texture. Mix in egg yolks and beat for another 2 - 3 minutes.
Stir in the marmalade, orange juice and milk. Fold in the sifted flour one third at a time until all combined well. Do not over mix the batter else cake would be tough in texture. Once all combined well stop mixing the batter and make sure no lumps of flour remain at the bottom of the bowl.
In a clean dry bowl beat the egg whites with an electric beater until they form firm/stiff peaks. Fold gently into the cake batter without deflating the egg whites.
Preheat the oven to 150 degree celsius. Grease 8 inch round tin and line it with parchment paper.
Pour the batter into the prepared tin and bake in the preheated oven for 35 minutes or until the tester inserted in the center comes out clean.
Remove from the oven and set aside on a wire rack to cool.
For pastry cream, in a heavy bottomed deep pan pour milk and add half of the sugar.
Put the pan over the low flame stirring occasionally.
Meanwhile in a wide flat bowl mix flour with remaining sugar. Add both the egg yolks to flour in the center and do not mix.
Once the sugar is dissolved in the milk stop stirring but keep the milk boiling.
After some time a layer of fat is formed on top of the boiling milk scoop out the same with a ladle and pour it over the flour on the sides. Do not pour the fat layer of milk in the center over the egg yolks otherwise they will be cooked.
Now mix egg yolks and flour mixture together and add some more milk. Mix nicely.
At last add all the batter to the boiling milk and keep on whisking vigorously. After 2 - 3 minutes a thick texture cream will start forming leaving sides of the pan. Remove from heat and transfer to a clean bowl.
Set aside to cool down at room temperature. This can be made in advance and stored in fridge.
Meanwhile in a clean bowl whip cream until stiff peaks form, fold this cream gently into the cooled pastry cream along with orange marmalade and orange extract.
For assembling, slice the cake half horizontally. Place the bottom half of the cake in a serving plate and spread half of the pastry cream over it. Cover with the top half of the cake. Use the remaining cream to cover the top.
Garnish with orange slice and peel.