Preheat the oven at 375°F
Put the eggs and powder sugar into your stand mixer's bowl set over a pan of gently simmering water (bain marie). Gently whisk until the powdered sugar has been dissolved
Using your stand mixer, mix using the whisk attachment. Whisk the mixture until it is thick and mousse-like, and leaves a trail when you lift the whisk
Sift the flour over the egg/sugar mixture and gently fold in with a spatula. Add the butter and fold – work quickly to prevent the mixture collapsing.
After the butter and flour have been incorporated into the mixture add 1 teaspoon of baking powder
Put parchment paper onto your baking tray and transfer the cake batter into a 10x15'' rectangle approximately
Bake for 10 minutes - check and add 2-5 extra minutes to get the cake into a light golden color
Once out of the oven, using the parchment paper roll the cake into a swiss roll (to prevent it from cracking once its cooled). Let it rest shaped for 1 minute.
If you feel the cake is a little dry prepare a symple syrup (equal parts of water and sugar dissolved over medium heat) and using a brush get the cake moist.
Using a spatula spread out 1 can of dulce de leche evenly including the borders.
Roll tight into a swiss roll and decorate as preferred!