In a pot of boiling water, boil whole potatoes for 25 minutes or until fully cooked. Do not cut or peel potatoes, as you want to keep as much water out as possible. Test doneness with a fork or knife. Remove cooked potatoes from water, pat dry, and let cool until safe to handle (but still warm).
Peel potatoes. The skin should pull right off, but parts may need to peeled with a knife or peeler.
Press potatoes through a potato ricer or mash with a potato masher into a large bowl. Do not put in a blender or food processor as this will overwork the potatoes.
Create a well in the potatoes and add the egg yolk, salt, and some of the flour. Stir with a fork and work it together, adding flour as you go, until all the flour is mixed in. Once the potatoes start to come together like a dough, stop using the fork.
Continue mixing with your hands until everything is fully incorporated. Press dough together into a ball. Dough may be sticky and this is okay, but if it's excessively sticky, add a little extra flour. Let rest for 5-10 minutes.
Divide dough ball into four smaller balls. Working with one ball at a time, roll out into foot-long logs. Cut each log into approximately 20 pieces, all about 1/2 inch wide. If you're not creating ridges on the gnocchi, these individual pieces can be transferred to a pan dusted with semolina or rice flour.
If creating ridges, roll each piece one at a time across a ridged gnocchi board or the back of a fork. Transfer pieces to a pan dusted with semolina or rice flour.
Gnocchi can be cooked in boiling salted water for approximately a minute. When they float, they're ready.If not cooking right away, transfer the gnocchi to the fridge.Gnocchi can be frozen for a few months. Transfer the pan to the freezer and let it sit until frozen. Then transfer gnocchi to a ziplock bag. (This process lets them freeze individually without getting stuck together.)
