For the Bolognese Sauce:

1. Make the Bolognese sauce 1 to 3 days in advance (head over here for the authentic recipe from Bologna, Italy).

For the Spincach Gnocchi:

1. Boil the potatoes: While the bolognese sauce is simmering, add the potatoes to a medium sauce pot cover with about 2 inches of water, and add salt to taste. Bring the pot to a boil and cook until fork tender (about 25 minutes). Strain the potatoes and use a fork to hold each potato steady while you use a knife or a spoon to scrape off the skins while they're still hot. Discard the peels, or use them to make homemade broth. *Alternatively, you may bake the potatoes until fork tender (about 1 hour at 400°F/205°C) if desired. 
2. Make the dough: In a large mixing bowl or on a countertop, mix the flour and salt together using your hand and make a well in the middle. Rice or grate the potatoes into the well while the potatoes are still hot to very warm (you'll see steam coming off of them), add the spinach, and stir everything together using a fork until mostly combined and crumbly looking. Add the egg yolk, stir just to incorporate it, and then bring the dough together using your hands.
3. Form the dough: Place the dough onto a non-stick baking mat (or a lightly floured work surface) and press it down slightly to form a larger rectangle. Fold the dough like a letter bringing in both sides to the middle. Flatten it once more and then fold in the opposite sides like a letter. Pinch the dough together and using your hands gently roll it into a 16-inch log. Divide it into 4 smaller logs (each about 4 inches long) using a floured bench scraper. The dough will still be warm at this point and feel like a cross between pasta dough and mashed potatoes (sturdy, but soft).
4. Let the dough rest: Place the upside-down mixing bowl over the tops of the logs to cover them and allow them to rest for 30 minutes to let the dough relax.
5. Cut the gnocchi: Working with one log at a time, roll the logs into long ropes and cut them into gnocchi or gnocchetti using a floured bench scraper or knife. Roll each gnocchi over a gnocchi board, cheese grater, or the tines of a fork while applying gentle pressure to make indentions in the dough or if the dough is really soft, just use a fork to make imprints on the tops. Place the gnocchi onto a lightly floured parchment-lined baking pan leaving space in between each and repeat with the remaining dough. *Alternatively, you can simply cut the gnocchi and press an indention into them using your thumb if you don't want to make the 'rigate' or ridges. 
6. Cook the gnocchi and assemble the dish: Cook the gnocchi in a large pot of boiling salted water just until they float to the top plus about 1 minute more (about 3 to 4 minutes). Add 1/1/2 to 2 cups of the Bolognese sauce (or more or less if desired) to a skillet set over medium heat, add the cooked gnocchi and a splash or two of starchy gnocchi cooking water and toss everything to coat. Sprinkle with grated cheese and serve. Enjoy!