In a large bowl, mix together a tablespoon of water, the cognac and the raspberry jam. Dip the lady fingers into this mixture and arrange them in the bottom of 2 tumblers. You may need to break the lady fingers in half to fit the bottom of the glasses.
Make the chocolate mousse: melt the chocolate in a bowl set over a pan of hot water. Allow the chocolate to cool slightly, then stir the egg yolks into it.
In a separate bowl, whisk the egg whites until they form stiff peaks. Carefully fold the egg whites into the chocolate mixture a little at a time until completely incorporated.
Lay some raspberries on top of the moistened lady fingers, then carefully spoon the chocolate mousse over them. Finish with a final layer of raspberries.
Chill in the fridge for a couple of hours or, better still, overnight. Allow to come to room temperature before serving, topped with custard if you like.
*Inspired by Sebastien T. featured in the Realfood Cookbook