Ukrainian
Whisk the egg whites to soft peaks, then add the 250 g of sugar a spoonful at a time and whisk to a stiff, glossy meringue.
Mix the chopped hazelnuts with the flour and fold them gently into the meringue with the vanilla.
Spread the meringue into two 22 cm circles on baking sheets lined with parchment and bake at 120C for 2 hours, until dry; cool completely on the paper.
For the cream, heat the milk with the 180 g of sugar and the egg yolk, stirring, until it thickens slightly (about 5 minutes at a bare simmer), then cool.
Beat the butter until pale, add the cooled milk mixture a spoonful at a time, then the brandy; put a third of the cream aside and beat the cocoa into the rest.
Peel off the paper, spread one meringue layer with about half of the chocolate cream, top with the second layer and cover the top and sides with the remaining chocolate cream.
Pipe the plain cream on top, dust with powdered sugar and chill for at least 3 hours before cutting with a sharp knife.