Cut a lid off 4 lemons. Cut the lemons slightly flat at the bottom. Carefully remove the pulp and press it through a cloth. Wash 1 lemon and finely grate the peel. Cook 350 ml water and 125 g sugar for about 5 minutes until bubbly. Add lemon juice and zest and bring to the boil briefly.
Pour through a sieve and freeze in the freezer for about 1 hour. Beat the egg white and 10 g sugar until stiff and fold into the sorbet. Leave to freeze for another 2-3 hours. Stir from time to time. Pour sorbet into a piping bag with a star-shaped spout and squirt into the lemons. Serve decorated with lemon balm