1 Blanch spinach and squeeze out excess moisture: Fill a medium saucepan halfway with water and heat until simmering. Add spinach and cook until tender, about 1 minute. Drain.
Let spinach cool enough to touch, then squeeze as much moisture as you can out of it. You can also use a potato ricer if you have one to squeeze the excess moisture out of the spinach.
2 Make the gnocchi dough: Add the spinach, egg, salt, and half of the ricotta to a food processor. Pulse until completely blended.
Transfer mixture to a large bowl, mix in the remaining ricotta and the Parmesan cheese. Stir a pinch of nutmeg into the flour.
Add the flour in by hand, starting with a half of the flour. Mix everything with your hands until the mixture holds together as a dough.
3 Knead the dough: Put the dough out on a lightly floured smooth, clean surface. Knead lightly for about a minute, adding additional flour if needed, if the dough sticks too easily to the board or your hands. (At this point, if you wrap the dough in plastic and refrigerate for an hour, it will be easier to roll out.)
When the dough is smooth and pliable, and still just a little bit sticky, divide it into 4 portions, each the size of an orange.
4 Roll dough out into long ropes, cut into pieces: Flour your hands lightly. Using both hands, and a light touch, roll the dough out with a back and forth motion, starting at the center and stretching the dough out, to form a roll.
This is the tricky part. You don't want to put so much pressure so that you compress the dough, but you do need enough pressure to create a rope of dough.
The trick is to stretch the dough sideways as you are rolling. Once the segment you are working on gets to be about a foot long, you may find it easier to cut it in half, and then start working on that smaller segment.
Roll the dough out until the roll is about the size of a middle finger. (Note that if your hands or the board is a little too floured, you may not have enough traction between your skin and the dough to easily stretch it sideways.) Cut each roll into 1-inch pieces.
5 Create indentations with a fork: Hold a fork at a 45% angle with its tines facing down on the work board, the curved part of the fork facing away from you. Starting with the curved outside bottom of the fork, press each piece of dough up along the length of the tines. Let the gnocchi fall back down.
This is a pretty quick motion, the result is an indentation of the fork tines on one side of the gnocchi, and an indentation of your fingertip on the other side.
Place the gnocchi on a lightly floured cookie sheet. At this point they can be cooked, or kept in the refrigerator several hours or overnight.
6 Cook the gnocchi in boiling water: To cook the gnocchi, fill a large wide pot half-way with water. Bring to a boil, add 1 teaspoon of salt for every quart of water.
Once the salt has dissolved, gently drop the gnocchi in the water, one by one. Try to do this in a way that the gnocchi are not falling in on top of each other, but rest on the bottom of the pan in a single layer.
As the gnocchi cooks, they will rise to the surface of the water after a couple minutes. Use a slotted spoon to remove the risen gnocchi from the pot, place in a serving bowl.
Sometimes the gnocchi can stick a little at the bottom. If you suspect this, nudge them a little to unstick them. As you remove some gnocchi, you can add a few more to the pan.