Mix the blackberries with the liqueur and sugar and let it steep for about 30 minutes. Mix the leaked juice with starch and bring to the boil briefly. Carefully fold in the blackberries.
Cut 16 mint leaves into strips, mix with egg yolk, sparkling wine and sugar in a mixing glass and strain. Beat the liquid over a water bath to form a wine foam cream.
Spread the blackberries with the thickened marinade in deep dessert plates. Cover with mint foam. Place a scoop of vanilla ice cream on top, garnish with almonds and a peppermint leaf each and serve.
A Beerenauslese or even an ice wine goes very well with this (Riesling or Ruländer are ideal because of their fruitiness).