To prepare the mousse, warm the chocolate, butter and coffee in a bain-marie to 45°C. Remove from the heat and whisk in the egg yolks until thoroughly combined and completely emulsified. Repeat the process with the warm water, adding in a steady stream

In a separate bowl, whisk the egg whites and sugar together to form a soft peak meringue. Gently fold the meringue mixture into the chocolate mixture, then pour into individual cups until ¾ full. Allow to set in the fridge

To prepare the sablé biscuits, cream together the butter and sugar until pale and fluffy. Slowly add the cream and egg yolk to the butter mixture, then fold in the flour, being careful not to overwork the dough

Divide the dough in half, wrap in cling film and chill in the fridge to rest until firm, for approximately 2 hours

Preheat the oven to 160-170°C/gas mark 3

Remove half of the dough from the fridge and allow to soften slightly, so the dough is not too hard. Roll the dough out on a smooth, floured surface to make a 1cm thick square. Transfer to a baking tray and chill in the fridge for approximately 20 minutes

Remove from the fridge and place in the oven for approximately 5 minutes, to pre-bake the dough. Remove from the oven, cut into 3 x 6cm rectangles, then return to the oven and bake for a further 5-10 minutes

Once baked, remove from the oven and allow to cool. The biscuits can be kept in an airtight container for up to 1 week, and any remaining dough can be frozen for up to 1 month

To prepare the coffee cream, blend together all of the ingredients - the mixture should resemble a very thick pouring cream. Once the mousse has set, pour over a layer of the coffee cream

Dust with cocoa or hot chocolate powder to finish and serve immediately with the sablé biscuits