While the water is coming to a boil, line a large plate with three layers of paper towels. Spread the ricotta onto the paper towels in an even layer. Place additional paper towels on top and press gently to soak up some of the moisture from the ricotta. Transfer the drained ricotta to a medium bowl.
Add the Parmesan, egg yolk, salt, and nutmeg to the ricotta and stir to combine.
Weigh your flour; or measure it by gently spooning it into a cup, then sweeping off any excess. Add the flour to the ricotta mixture and stir to form a cohesive, slightly sticky dough.
Transfer the dough to a floured surface, sprinkle lightly with additional flour, and shape into a 5" square.
Divide the dough into four roughly equal pieces.
Working with one piece at a time, use your palms to roll the dough into a 1/2"-thick log about 18" to 20" long. Sprinkle with additional flour as needed to prevent sticking.
Using a sharp knife or bench knife, cut the log crosswise into 1/2" pieces. If the dough begins to stick to your blade, sprinkle the blade with additional flour.
Gently transfer the gnocchi to the prepared baking sheet. Jiggle the baking sheet to coat the gnocchi in flour and prevent them from sticking together.
Once all the gnocchi are shaped, gently add about a third of them to the boiling water; stir immediately to prevent the gnocchi from sticking to the bottom of the pot or to each other. Once they have all floated to the surface, about 30 seconds, allow them to cook for an additional minute.
Use a slotted spoon or strainer to drain the gnocchi and add them directly to your sauce of choice.
Repeat with the remaining gnocchi. Serve immediately.
Ricotta gnocchi are best enjoyed as soon as they’re made. To prepare them in advance, freeze the shaped gnocchi in a single layer on a flour-dusted baking sheet until solid, then transfer to an airtight container and freeze for up to 3 months. Cook the gnocchi directly from frozen; gnocchi may need an additional 30 to 60 seconds of cooking time.