Puree the prepared nectarines, deseeded, peeled and cut into pieces, very finely in a suitable saucepan. Add the sparkling wine and the preserving sugar, stir well and bring to the boil. After the cooking time has started, cook for about 3 minutes, stirring constantly. Then make a gel test. Only when the jam is firm in the sample, fill it to the brim in 5 200 ml jars with screw caps (twist-off jars) and close them immediately.
They should stand on their heads for a quarter of an hour, then carefully turn them over and ideally let them cool well overnight.
I always use gelling sugar 3: 1 with this jam so that the jelly doesn`t stay too soft.