No matter how many new desserts come along, the classic chocolate mousse is rarely met with anything but delight. There are two main types, one set with gelatine (more correctly known as a cold soufflé) and the one that is so thick you can barely get your teaspoon in.
Snap 250g of fine dark chocolate into a heatproof bowl, place it over a pan of simmering water and leave to melt. Stir in 40g of butter and 2-3 tbsp of espresso coffee. Remove the melted chocolate from the heat and separate 4 eggs. Stir each yolk into the melted chocolate carefully then beat the whites until they are thick and fluffy. Fold the egg whites into the chocolate and refrigerate for 3-4 hours until set. The longer you leave it, the thicker it will be.
Avoid stirring the chocolate as it melts, which can make it "seize". Turn off the heat as soon as it is melted. Fold the egg white into the melted chocolate with a large metal spoon. It is easier than with a thick wooden one, which is also likely to knock the air out. Make sure that you leave no bits of egg white unmixed, at the same time taking care to treat the mixture gently. If you over-mix you will end up with a flat mousse.
As well as the espresso in this recipe – so good for bringing the flavour of the chocolate out – it is worth considering other flavourings, too. Try a little rum or brandy, or an eau de vie such as framboise (in which case serve a few exquisite raspberries on the side). You can also experiment with flavoured chocolate, such as those spiked with finely chopped praline or ginger.