Prepare the Oven: Move your oven rack to the middle and preheat the oven to 350 F. Line your 10 x 12 pan with parchment paper and generously spray with nonstick oil.
Whisk the egg whites: Separate egg whites from the egg yolks. Put the egg whites in the stand-up mixer bowl. Attach the bowl containing the egg whites and mix on medium-high speed until stiff peaks.
Mix the flour: In a small bowl, mix the flour, baking powder, salt, and cocoa powder. Mix using a wire whisk. Set aside.
Mix the wet ingredients; Place the egg yolks in a large bowl and add the sugar. Mix until pale in color. Add the melted butter. Add half of the whipped egg whites and fold gently together.
Add wet and dry Ingredients: Add the flour mixture to the egg yolk mixture and gently add the rest of the whipped egg whites. Fold using a spatula until there are no white streaks present.
Bake the Cake: When ready, pour in batter mixture into the prepared baking sheet and bake for ten to fifteen minutes. Start checking the cake using the toothpick method starting in ten minutes. When the toothpick comes out clean, then take it out from the oven. While the cake is still hot, scrape the sticking side of the cake off using a knife.
Sprinkle the top of the cake with powdered sugar and cover it with a towel. With one end of the towel extending about 2- 3 inches out of the cake. Put a cooling tray on top and flip the cake.
Remove the parchment paper. Very gently roll the cake and let it cool. Sometimes the cake may break, but you will cover it with the ganache, so don't fret.
When the cake is cool, unfold the cake and fill the whole cake with the filling leaving 2- 3 inches on one end unfilled. Very gently roll the cake tightly and the wrap with wrapping plastic and refrigerate until ready to fill.