Wash the lemons, dab dry and halve lengthwise. Squeeze lemon halves carefully, put halves aside. Fill lemon juice (approx. 1/8 litre) with water to 1/2 litre liquid.
Bring lemon water and sugar to the boil. Let the liquid cool down a little. Cut mint into fine strips and stir into the mixture. Place in the freezer for 4-5 hours, stirring occasionally. Remove the remaining pulp from the lemon halves that have been set aside.
Freeze the lemon halves. Fill iced lemon halves with the lemon ice and serve. Decorate with mint leaves.