Clean, peel and cut the pineapple into pieces. Select the raspberries, wash if necessary and put them in a bowl together with the pineapple pieces. Mix lemon juice, sugar and rum and pour over the fruit.
Mix carefully and leave to marinate for 30 minutes. Use an ice-cream maker to form ice cream scoops and arrange on dessert plates together with the fruit salad. Serve as desired, decorated with pineapple slices, lemon balm and lemon peel strips.