Cut the ginger unpeeled into relatively large cubes and place in a bowl. Then peel 5 limes and add the peel to the ginger and sprinkle with the sugar. Squeeze these 5 limes and pour around two thirds of the juice into the bowl. Lightly crush everything with a mortar (or potato masher) and let it steep for about 15 minutes.
Pour in the prosecco and season to taste. Add a little sugar or the rest of the lime juice, depending on your taste.
Pour through a sieve into glasses, add ice cubes as desired and garnish with slices of the last lime and sprigs of mint
Tip: grated instead of diced ginger intensifies the taste. And of course you can also use mineral water instead of Prosecco.