Prepare the brioche dough 12 hours ahead, following the brioche recipe. When ready to use, rid the dough of all the air it contains, knead it into a ball, then roll it out into a 11 inch wide disk, about 1/4 inch thick. Rest it on a buttered and floured oven tray and leave to rise for 1 hour at room temperature. Bake in a hot oven (410 F), for 20 to 25 minutes. Leave to cool. Slice the brioche in half horizontally. Brush both halves with a few drops of kirsch or rum. Spread the cold pastry cream over the bottom layer, then cover with the top half. Dust the surface with some confectioner╒s sugar. For the pastry cream: combine the sugar, the yolks, the flour, the vanilla sugar and whisk until smooth. Add the boiling milk, stirring constantly. Pour the mixture back into a saucepan and boil for 1 minute. Leave the cream to cool off, covering it with some buttered parchment paper, to prevent crusting.
