Drain the pineapple rings and collect the juice. Mix flour, 2 tablespoons of pineapple juice, Amaretto and mineral water until smooth. Add egg. Let dough rest for about 1/2 hour. Heat some oil in a pan and pour in 1/4 of the dough.
Fry on both sides for about 2 minutes. Do the same with the rest of the dough. Arrange on plates with one cut pineapple ring each. Dust with icing sugar and serve garnished with lemon balm leaves.