250 g (8 oz) white chocolate (30% cocoa solids), broken into small pieces
crushed seeds from 4 green cardamom pods
200 g (7 oz) mascarpone cheese
3 egg whites
white chocolate curls, to serve
cocoa powder, for dusting
Place 6 small ramekins in a freezer. Pour the milk into a small saucepan and add the lemon grass. Bring to the boil, then remove from the heat and leave to stand and infuse for 5 minutes.
Meanwhile, melt together the chocolate and crushed cardamom seeds in a heatproof bowl set over a saucepan of gently simmering water, stirring occasionally. Remove from the heat.
Strain the warm milk into the melted chocolate and stir well. Beat in the mascarpone with a hand-held electric whisk until smooth, then chill.
Whisk the egg whites in a clean bowl with a hand-held electric whisk until stiff, then gently fold into the chocolate mixture. Spoon into the ramekins and place in the freezer for 5–10 minutes before serving. Alternatively, to make ahead, cover and chill in the refrigerator until required.
Top with white chocolate curls and dust with cocoa powder and serve.