• Peel the cooked russets and grate them. Spread the potatoes out on a baking sheet for a few minutes for any moisture to evaporate.
• Place a large pot of salted water to boil for cooking the gnocchi.
• Place the russets in a bowl and add the yogurt or aquafaba and salt. Mix until everything's evenly dispersed, then begin kneading in the flour. First add a cup and knead, then add a bit more as needed until you have a smooth dough.
• Pinch off a portion of the dough and use your palms to roll it into a ½ inch thick cylinder.
• Use a knife or bench scraper to cut off ½-inch lengths of the cylinder.
• Press each piece of the dough, cut side down, on the tines of a fork, while pressing with your thumb on the other side of the dough to make an indentation. Roll it off gently and place in a baking sheet. Repeat with the remaining dough.
• To cook the gnocchi, let the water come to a rolling boil. Add the gnocchi, a few at a time, and stir gently. The gnocchi will let you know they are done by floating to the top. Scoop them out with a slotted spoon and set aside.

Make the sage butter sauce

• In a saucepan, heat the butter with the garlic and 1 tablespoon sage.
• When the butter melts, add the mushrooms, if using, and season with salt and ground black pepper. Saute the mushrooms until they begin releasing their juices, a couple of minutes. If not using mushrooms proceed directly to next step.
• Add the gnocchi to the pot with the remaining sage and cook, stirring frequently, until the gnocchi begin to turn golden-brown. You can let them brown as much or as little as you like.
• Season with salt and ground black pepper as needed.
• Serve hot or warm with vegan parmesan for sprinkling.