Melt the white chocolate in a heatproof bowl over a pan of simmering water, stirring gently. When it’s melted, set the bowl aside to cool down a little.
In another bowl, beat the cream, egg white and peppermint to soft peaks with an electric hand whisk.
Put a big dollop of cream onto the slightly cooled chocolate mixture and mix thoroughly, then gently fold the chocolate mixture back into the cream.
Divide the mixture between 6 small glasses, like the ones shown. Chill in the fridge for a couple of hours, or give them a fast icy zap by sitting them in the freezer for 10-15 minutes. Decorate each glass with a mint sprig, and serve.