If I have a lot of spare egg whites at home I usually make this fake bird's milk, but if there are egg yolks left over, you can of course add them to the custard.
Start heating the milk in a saucepan.
Add the flour to the vanilla pudding mix, add it to the milk with a hand whisk (stirring continuously). Add the sugar and vanilla sugar, stirring continuously until thick.
Beat the egg whites with the salt and vanilla sugar until stiff, scoop out with a spoon . You can also put it in boiling water, or the easier way is to scoop it out onto a plate and put it in the microwave for 1-2 minutes at 700 watts.
Once the egg whites have set, fold them into the vanilla custard and you're done. When it is cool you can eat it.