Mix the jelly powder in a saucepan with 1/2 litre of cold water. Leave to swell for 5 minutes. Add sugar. Heat while stirring until everything is dissolved. Do not boil! Peel and slice bananas and sprinkle with lemon juice. Divide into 4 glasses.
Pour jelly over them. Put it in a cold place until it is firm. Before serving, whip cream until stiff, sprinkle with vanilla sugar. Pour into a piping bag with star-shaped spout. Spray on the food. Sprinkle with chocolate shavings