Prepare gelatin according to instructions on package (soak leaves in cold water. Melt in a saucepan over mild heat with little liquid). Crush the mango pieces and stir through with yogurt, sparkling wine, juice of one lemon and vanilla. Stir the gelatin mixture into the mango mixture and finally fold in the whipped cream.
Moisten the rim of the shells with juice of one lemon and press into sugar. Fill the mango mixture into the bowls and decorate with the pistachio nuts and lemon balm.
Tip: Use creamy natural yogurt for an even finer result!