Place a large pot over high heat, add the potatoes, cover with water and let them boil until soft. Drain completely.
Transfer the boiled potatoes to a bowl and mash with a fork into a smooth purée. In the same bowl, add the flour, Parmesan, egg yolks and nutmeg, and season with salt and pepper. Mix with your hands, wearing disposable gloves, until the mixture is homogeneous.
Transfer the mixture to a pastry bag and create a line of about 30 cm / 12 inches on a floured kitchen counter. Lightly flour the line of mixture and cut into pieces about 2-3 cm (1 -1¼ inch) . Repeat the process for all the mixture.
Flour a baking pan, carefully place all the pieces in it and lightly flour them.
Place a pot of water over medium to high heat. Fill a bowl with water and ice and set aside. When the water begins to boil, place in the gnocchi in batches and let them boil until they rise to the surface. With a slotted spoon, transfer them to the bowl of water and ice and leave them until they cool.Transferring the gnocchi to iced water stops the gnocchi from overcooking and falling apart. Once cooled, transfer to a baking pan, drizzle with a little sunflower oil and mix them so they are coated in the oil and do not stick together. Follow the same procedure for all the gnocchi.