Bring a kettle of water to the boil. In the meantime, add 2 large handfuls of ice cubes (around 500g) to a large bowl and pour in enough cold water to almost reach the top of the ice.

Break the chocolate into a medium bowl (that easily fits into the large bowl) and pour over 210ml of boiling water (don’t exceed this amount or the mousse won’t hold its shape). Whisk it until the chocolate has completely melted.

Now place the bowl with the chocolate into the bowl with the ice and whisk until the chocolate begins to thicken (4-5 minutes), thereby incorporating air. Once it has thickened to a point where the whisk leaves thick ribbons and the surface doesn’t instantly level out when you drizzle the chocolate, remove the bowl from the ice and continue whisking for another 30 seconds as it cools down even further. This happens really quickly, so rather remove it too early and continue whisking it to see if it stiffens up into a mousse. If not, return it to the ice bath and cool it down a little more.

Either spoon the mousse into a glass or serve it on a plate. To do this elegantly, soak a tablespoon in very hot water to heat it up. Then make a quenelle by pushing the warm spoon through and finally around the chocolate mouse for a smooth egg shape.