Mix the sifted flour with the coffee and baking powder.
Beat the melted butter with the powdered sugar into cream. Add the yolks 1 by 1 and beat well. Separately, beat the egg whites to snow.
To this mixture, add the flour, walnut and egg white mixture in lots - stir lightly with a spatula.
Transfer the mixture to an oven dish laid out with baking paper and bake about 30 min. in a preheated 338°F (170 °C) oven. You can check to see if the cake is ready with a toothpick.
Once it cools in the oven dish, transfer the cake to a suitable platter.
Syrup it with the cognac/water mixture and once it absorbs the syrup, sprinkle it with grated white chocolate.