Separate the egg. Beat egg white until stiff. Mix egg yolk and 5 tablespoons of cream. Stir 1/8 litre milk and starch until smooth. Heat the remaining milk. Break Toblerone into pieces. Chop 2 pieces finely and melt the rest of the Toblerone in the hot milk.
Bring to the boil while stirring, stir in cornflour and bring to the boil again briefly. Remove from heat, first stir in the egg yolk-cream mixture, then fold in the beaten egg white loosely. Spread the mixture into 4 dessert glasses and let it cool down.
Cut the banana into slices, sprinkle with lemon juice and sprinkle with sugar. Lightly whip the rest of the cream. Just before serving, put 2-3 banana slices and a dollop of cream on each dessert.
Sprinkle with chopped Toblerone and serve decorated with mint.