1) Place the egg whites in a large mixing bowl and whisk together by hand or with an electric whisk until thick peaks form. Stir through the remaining mousse ingredients until smooth. 2) For the chocolate sauce: whisk all the ingredients together in a small saucepan over a gentle heat until a smooth sauce is formed. 3) For the mixed berries: mash the berries and water together until a loose mix is formed. 4) For the citrus and nuts variation: mix the zest or nuts through your mousse. 5) To serve: divide the mousse amongst five glasses, cups or ramekins. Drizzle over the chocolate sauce or mixed berries as you like.