Working very gently with a wooden spoon or spatula, mix into the puréed potato a generous pinch of salt, the egg (optional) and enough flour to make a smooth, soft and only slightly sticky dough. Do not knead the dough or it will become gummy, just mix the ingredients together as gingerly as you can. Form the dough into a ball and place it on a well floured surface.
Then break off a handful of the dough and roll that with both hands until you have a ‘rope’ about the thickness of your thumb.
Cut this rope into 1 inch lengths. Take each bit of dough and flip it with your index finger against the inside of a fork (or if you have one, the special Rigagnocchi, or ‘gnocchi paddle’ pictured below, which you can find in some specialty food shops). This will cause the gnocchi to take on a concave shape with ridges on the outside, which will ‘catch’ any sauce you put on them.
Cook the Gnocchi in gently boiling well-salted water. They are done just as soon as they rise to the surface of the water.