First of all, wash the potatoes well and boil them for about 35 minutes or until they are well cooked (the tines of a fork must be able to go in and out easily).

In the meantime, clean the black cabbage by removing the internal ribs of the leaves, then cut it into pieces.

Rinse it, then blanch it for 5-8 minutes (it should be soft) and drain it.

Once well cooked, drain the potatoes, peel them and mash them immediately with a potato masher, while they are still hot.

Separately, blend the black cabbage after having squeezed it well.

Add cabbage, egg yolk and salt to the potatoes and mix, then add the flour: you should obtain a compact but not too dry dough.

Take a little dough at a time and form long strings about 2 cm thick, then cut them into pieces about 3 cm long.

Pass the gnocchi on the floured tines of a fork to obtain the typical striped appearance.

That’s it: your black cabbage gnocchi are ready.

Boil plenty of water with a little salt in a large pan and, when it boils, add the gnocchi and mix immediately.
In the meantime, melt the butter with the chopped sage in a large non-stick pan: when the gnocchi rise to the surface, drain them with a slotted spoon directly into the sauce, then mix in the cheese.

The black cabbage gnocchi are ready, all you have to do is plate them and serve them, perhaps with some freshly grated pepper.