Boil the potatoes until they become really soft (about 20-30 minutes, depending on the size).
Drain, peel and mash the potatoes evenly, then add the flour when they are still warm (overwise they'll become sticky). Mix well until you get a nice soft non-sticky dough.
When you have an even dough similar in consistency to the bread dough, cut it in smaller parts and roll them with your palms to get a long roll thick about 2 cm of diameter (1 in.). Keep the surface and the dough smooth with flour to prevent stickiness.
Now with a dough-cutter cut the gnocchi about 2-3 cm long. (You can then roll them on a fork to get the typical gnocchi lines). Let them rest separated.
In a large pot bring to boil salted water and toss the gnocchi one by one so they won't stick. It will take 1-2 minutes to cook.
Meanwhile melt the butter in a large pan with the sage leaves.
As soon as the gnocchi float to the surface, it means they are ready to go! Take them out with a skimmer and toss them in the pan with the melted butter.
Add the zucchini flowers, tos and serve with grated Parmigiano cheese.