Soak the gelatine. In the meantime, clean, rinse and cut the strawberries.
Peel the banana and cut into slices. Add sugar and juice of one lemon to the fruit form and blend everything together with a hand blender.
Melt the gelatine in 2 tablespoons of hot water and stir into the fruit puree. Whip the cream with vanilla sugar until stiff, stir the rum into the whipped cream.
Take 1/3 of the fruit puree, fold the rest into the whipped cream. Make sure that the fruit puree is folded in gradually so that the mousse remains creamy. Fill the fruit cream and the remaining fruit puree in layers into 4 dessert glasses. Leave to cool for about 2 hours.