In a medium saucepan, cook the potatoes in water until they are just tender, then drain and leave them in the pot to cook off any remaining water. Make sure there is no remaining water in the pot and cool the potatoes to a lukewarm temperature.
Place 1/2 of the potato into a blender with the cheese, butter, salt and pepper and blitz until the mix is just combined.
In a large bowl, mash the remaining potato and transfer the potato and cheese mix from the blender into the bowl before mixing in the flour and the sage.
On a well floured surface, roll the dough with a rolling pin into a rectangle that is 1/4 of an inch (0.64 cm) thick.
With a knife or a bench cutter, cut the dough into 8 or 9 evenly spaced strips and then cut them in the opposite direction to create small squares about 0.75 inches (2cm) wide. Lightly roll each piece on a board or fork to create the typical gnocchi look.
Place each piece of gnocchi onto a sheet of baking paper and let it sit uncovered while preparing the remaining gnocchi.
Bring a saucepan of water to a rolling boil and cook the gnocchi for 3-4 minutes without overcrowding them and until they float to the surface. Use a slotted spoon to transfer the cooked gnocchi to a large serving bowl.
In a large frying pan on medium heat, cook the butter, salt and the sage leaves for about minutes until the butter browns nicely without burning and the sage leaves are slightly crisp.
Pour the browned butter and sage over the gnocchi and serve.
If you prefer you can fry the gnocchi for a couple of minutes in the pan to brown them before serving or reheat any leftovers this way the following day.
Note: Each batch may vary depending upon the potatoes and how wet they are. Add a little more flour if the dough is too wet.