Preheat the oven to 400°F.
Poke the potatoes with a fork and bake them for 1 hour or until they are tender.
Peel the potatoes and pass them through a potato ricer into a large mixing bowl.
Add the egg yolk, salt, and flour until a dough forms. Refrain from overworking the dough.
Prepare a clean work surface with flour and divide the dough into 4 equal pieces. Roll each piece into a long, thin log about 3/4 inch in diameter. Cut each record into 3/4-inch slices and gently press each piece with a fork to create ridges.
Bring a large pot of salted water to a quick boil. Cook the gnocchi in batches until they float to the surface, then cook for another 15-20 seconds.
In a separate pan, melt the unsalted butter over medium heat. Then add the sage leaves and cook for 1-2 minutes until the butter is browned and the sage leaves are crispy.
Remove the sage leaves from the pan and set aside. Place the gnocchi to the pan and toss until coated in the sage butter sauce. Cook for an additional 1-2 minutes until the gnocchi is slightly crispy and browned.
Season with salt and pepper to taste and sprinkle with freshly grated Parmesan cheese and crispy sage leaves. Serve immediately.
