Grease 2 9x13 baking sheets or pans, line with parchment paper, and grease that too
preheat the oven to 350˚
sift the cocoa powder into a mixing bowl, cut up the soft butter into the bowl, and add a pinch of salt
add boiling water whisk to combine, stir until smooth, set aside
separate the eggs and put the yolks in a mixing bowl and the whites into the bowl of a stand mixer
use a hand mixer to beat the egg yolks with half of the sugar until soft and pale yellow, stir the chocolate mixture into the egg yolks
beat the whites on high until stiff peaks form
slowly add the remaining sugar until its incorporated
take a large metal spoon and fold a spoonful of the whites into the yolks bowl, stir to loosen the mixture
then fold in the remaining whites
to fold use a metal spoon, swirl around the bowl once, cut down through the middle, turn the bowl 1/4 of the way around, repeat, and keep on until no more white remains
spread in the prepared pans
bake 12-18 minutes JUST until the cakes spring back
cool on cooling racks with a damp towel over the top of the pan, not touching the cake
make the filling by beating the butter with the sifted powdered sugar
add the extract of your choice beat again until smooth and fluffy, if it's too stiff add a teaspoon of milk or two until the mixture is soft and fluffy
remove cakes from their pans lay on clean tea towels peel off the parchment paper
cover each cake with 1/2 the filling
starting from the short of one cake roll up the cake to the middle of then roll the other short side in
cut the cake between the rolls, then cut each roll into 3 equal pieces
lay on a baking sheet seam side down
repeat with remaining cake
chill in the freezer or fridge until ready to coat
to coat chop the chocolate, put in a heat safe bowl over a pan of simmering water until melted
lay cakes on a baking rack, over a baking pan
use a spoon to gently cover each cake, chill again
melt the white chocolate the same way and drizzle over the rolls
chill until ready to serve