Bring water to a boil in a large pot. Add potatoes and cook until a bit overcooked. Drain potatoes and pass them through a potato ricer (you can also use the larger holes of a cheese box grater) into a clean bowl or clean surface.
Sprinkle flour on a clean surface and place potatoes on top. Form a hole in the middle of the potatoes and add the egg yolk. With a fork, start scrambling the egg and start incorporating flour a little at a time. Season with a pinch of salt. Once the egg and flour are combined, begin folding in the potatoes until the dough is formed. (Tip: If the dough is too wet/sticky add small amounts of flour until the consistency is correct)
Boil salted water in a large pot for the gnocci. In the meantime, take about 1 cup of dough at a time and roll it out using your fingers to about 3/4 inch rope. Using a clean knife (I like to use the back--i.e. not the sharp part; you can also use a fork, or another blunt surface) and cut dough into 1/2 inch pieces. Dust pieces with flour as you go.
Prepare a bowl with water and ice and set aside. Working in batches, drop pieces into the boiling water and cook until they float, 1-2 minutes. Remove with a mesh skimmer or slotted spoon and place into the ice bath for a few minutes. Drain the water and toss with some canola oil to prevent sticking while you start the sauce.
In a large sauté pan on low-medium heat, combine chicken stock, heavy cream, pumpkin puree, parmesan cheese, nutmeg, and chopped sage. Season with salt and pepper. Let simmer on low heat for about 8-10 minutes.
In the meantime, add about 1 tablespoon of canola oil to a small sauté pan. Once the oil is hot, fry the 6 sage leaves for about 5-10 seconds on each side and carefully remove and place on a paper towel to remove excess oil.
Add gnocchi to the sauce until they are heated all the way through. Top with parmesan cheese and the fried sage to serve!