Shake out elderflower umbels and wash briefly in standing water. Put the flowers on kitchen paper and let them drip off. Boil up sugar and 3 litres of water. Wash lemon, grate dry and cut into slices
Put lemon slices, lemon acid and flowers in a large bowl and pour the sugar syrup over them. Leave the syrup to cool, then cover and leave in a cool, dark place for 3-4 days
Strain the syrup through a cloth and fill into bottles. Seal bottles well and put them in a cool place. The syrup will keep for about 6 months in the refrigerator. Fill the syrup with sparkling wine (approx. 1 part syrup and approx. 4 parts sparkling wine or mineral water for 1 250 ml). Cool to taste with raspberry ice cubes
waiting time approx. 3 days