Bake the potatoes: Set a rack in the middle of the oven and preheat to 400°F/204°C. Scrub and dry 20 ounces russet potatoes, then prick them all over with a fork. Transfer to a parchment-lined baking sheet and bake for 1 hour, or until completely fork tender.
Rice the potatoes: Peel the potatoes while they are still warm, but cool enough to handle. Pass through a ricer (or food mill) and allow to cool until no warmer than lukewarm temperature. My riced potatoes yielded about 13.7 ounces. Note: If the riced potatoes weigh significantly more or less than 14 ounces, you will want to re-measure the flour so that it's ¼ the weight of your potatoes.
Make the dough: On a large wooden surface (or in a large mixing bowl) combine potatoes and 1 large egg yolk with a fork. Sprinkle 100 grams all-purpose flour and 5 grams Diamond-Crystal Kosher Salt on top of the mixture, then use your hands or a bench scraper to begin cutting the flour into the egg-mixture. Knead for about 30 seconds - 1 minute until a shaggy mixture has formed. Continue mixing, gently, until it comes together into a rough rectangle. It will NOT be perfectly smooth. If the dough feels very sticky, gently knead in the remaining flour. Dust the top and bottom of the rectangle with a generous amount of flour.Note: You do *NOT* want to over-knead, which can lead to sticky, gummy, and/or dense gnocchi. The dough *will* be a bit sticky - that's fine! As long as it feels like a solid, mostly homogeneous mass, you should be good to go.
Optional - Test the Gnocchi: If this is your first time making gnocchi, I recommend the boil test! Bring a pot of water to boil. Cut a ½-inch square of gnocchi. Using your thumb, indent it slightly. Add the dumpling to the water, and cook for 1 ½ - 2 minutes, or until soft and tender; the gnocchi should be floating on the surface of the water. If it held together and didn't disintegrate, great! You're good to proceed to the next step. If it did disintegrate, you will want to add a bit more flour and gently knead to help the dough come together. Test again.
Roll Out the Gnocchi:
Line 2 large baking sheets with parchment paper and dust generously with semolina flour.Using the bench scraper (or a knife), slice the dough into 1 ½-inch wide portions. Roll each portion into a rope, about ½-inch thick. Dust with more flour, then slice into ½-inch pieces to form the shape of a pillow.
Optional - For a Ridged Texture: Using the side of your thumb, roll each piece against a flour-dusted gnocchi board or the back of the tines of a fork, rolling and flicking the dough to form a curled, cupped shape on one side and a ridged surface on the other. Continue dusting the board with flour as needed to prevent sticking. Note: Gnocchi can be delicate, so make sure to very gently roll them against the gnocchi board. If you don't want a ridged texture, I recommend indenting each "pillow" slightly with your thumb. The cup shape holds sauces better. Transfer each piece to the baking sheet, making sure they don't touch.
Boil & Serve:
Bring a large pot of salted water to a boil. Once boiling, add the gnocchi in batches. Once the gnocchi float to the top, cook for an additional 30 seconds to a minute or so until they're tender. Transfer them to the skillet with a slotted spoon, and toss to combine. You can add a little pasta water if necessary to thin out the sauce. Serve with your desired sauce, and enjoy! Alternatively, you can also pan-fry the gnocchi after boiling for a crisper texture.Note: Avoid a *vigorous* boil, which can cause the gnocchi to disintegrate.
Notes
Don't Over-Knead: This may feel counterintuitive, but the more you work the dough, the stickier it will feel. What's more, over-kneading can lead to a denser, gummier result.
Storage Instructions: Once you shape the gnocchi, you'll want to cook them within 20 minutes or so (otherwise, they begin to stick). Leftover cooked gnocchi can be stored in an airtight container in the fridge for 1 - 2 days. I recommend lining the container with layers of parchment paper, and evenly arranging them so they aren't touching.
Freezer Instructions: To freeze gnocchi for long-term storage, cook in boiling water until they just begin to float. Air-dry on a clean kitchen towel, then transfer to a parchment paper-lined baking sheet. Freeze for 1 hour until solid, then transfer to an airtight Ziploc freezer bag for up to 1 month. Cook frozen gnocchi in boiling water (do not thaw) until they float again.