Bake the potatoes for an hour until they are crispy on the outside and fluffy on the inside. Cool for a couple hours, remove insides with a spoon, and mash them, using a potato ricer or a fork, until they are very smooth.
Place the potatoes in a bowl and add the nutmeg, salt, a pinch of pepper, the egg yolk, and the ricotta. Mix together to combine and let rest overnight in the refrigerator, uncovered.
The next day, spread the semolina flour in an even layer on a baking sheet or tray.
Then place the potato mixture in the bowl of a stand mixer and, using the paddle attachment, add the flour on low-medium speed. Once the mixture has come together, remove it from the bowl and cut into fist-size balls.
Roll each ball in the palms of your hands and then form it into a cigar shape. Cut each of these tubes into 1-inch pieces. Place them on the bed of semolina flour and put the tray into the refrigerator for 10-20 minutes to set.
To cook, drop the gnocchi into salted boiling water. When the first few rise to the top of the pot, remove all the gnocchi with a slotted spoon.