Wash a lemon, dab dry and finely grate the peel. Bring 300 ml water, sugar and lemon peel to the boil while stirring until the sugar is completely dissolved. Leave to cool.
Squeeze both lemons. Beat the egg whites with the whisks of the hand mixer until stiff. Mix sugar syrup, lemon juice and beaten egg whites. Pour into a bowl and freeze for 2 1/2-3 hours.
Stir several times. In the meantime, wash the mint, dab dry, pluck leaves from the stalks and, except for a few for decoration, cut into strips. Remove sorbet from the freezer 20-30 minutes before serving and stir in the mint strips.
Pour the sorbet into four dessert glasses and serve decorated as desired with remaining mint leaves, lemon slices and lemon peel.