Wash the nectarines, cut them in half and remove the stones. Put one nectarine aside for decoration, cut the rest into small pieces and mix with 1 tablespoon of sugar and the lemon juice.
Mix the mascarpone with the quark, bourbon vanilla sugar, 75 g sugar and the milk.
Place half of the cantuccini in four dessert bowls, drizzle with half of the sherry and orange juice. Spread half of the mascarpone cream on top, then layer half of the marinated nectarines. Place the remaining cantuccini on top, drizzle with sherry and orange juice, spread the remaining marinated nectarines on top and finish with the remaining mascarpone cream. It is best to let the dessert steep overnight or for at least 3 hours.
Before serving, cut the remaining nectarine into thin slices and serve on top of the dessert. Decorate with lemon balm leaves if desired.