Briefly scald the kumquats with boiling water and rinse. Cut the drained into very thin slices. Remove the seeds in the process.
Boil the sugar with 150 ml of water, add the slices and simmer gently for 20 minutes over a mild heat. Remove the kumquats from the heat and let them cool in the syrup. Pour the syrup into a jug and chill.
To serve, put 1-2 ice cubes in 12 larger champagne glasses. Distribute the kumquat syrup between the glasses and pour the sparkling wine on top.
The finished syrup can be kept covered in the refrigerator for about 3 days, so it can be prepared well.