Squeeze the lemons and measure 200 ml lemon juice. Mix juice and sugar in a pot. Stir until the sugar has dissolved. Then reduce to a syrupy consistency, allow to cool
Add Prosecco. Beat egg whites until very stiff and fold in. Let the mixture set in a metal bowl in the freezer for 4-5 hours. Stir vigorously with a whisk about every 30 minutes
Wash the strawberries, clean and chop up to 1 strawberry. Puree the strawberry pieces, vanillin sugar and jam
Cut 1 strawberry into 4 slices. Divide the lemon sorbet between 4 glasses. Add strawberry sauce. Decorate with strawberry and lemon slices