Melt the dark chocolate gently in a bowl over a pan of simmering water.
Beat the egg yolks and most of the sugar together until creamy and pale.
Whisk the cooled melted chocolate into the egg yolk and sugar mixture.
Melt the unsalted butter in a pan over a low heat.
Whisk the melted butter into the chocolate mixture, adding a little water if too thick.
Whisk egg whites with the remaining two teaspoons of sugar until soft peaks form.
Carefully fold the egg whites into the chocolate mixture using a metal spoon.
Spoon the mixture into ramekins and refrigerate for two hours.
Top with crème fraîche, fresh cherries, and a dusting of cocoa powder before serving.