To make the gnocchi: Bake or microwave the potatoes until soft. Peel the warm potatoes and press them through a ricer, or mash them; measure out 1 1/4 cups (266g) potato; enjoy the rest as you see fit., Mix the baking powder with the flour, and sprinkle over the potatoes., Add the cheese, yolks, salt, and nutmeg, mixing just until everything comes together in a smooth ball., Place the dough on a floured work surface, cover, and let it rest for 30 minutes., Take about a third of the dough, and roll it into a rope about the thickness of a finger., Cut 3/4"-long pieces. Using a gnocchi board or the back of a fork, roll the individual gnocchi to create ridges on one side, and a little space in the middle., Place the gnocchi on a parchment-lined baking sheet dusted with flour, cover lightly, and chill until ready to cook. Gnocchi may be stored in the refrigerator up to a day, and in the freezer for several months., To cook: Bring a large pot of salted water to a boil. Reduce the heat to maintain a slow boil, and add the gnocchi., Once gnocchi float to the surface, cook for 4 to 5 minutes. Drain cooked gnocchi, and toss with sauce., To make the gorgonzola cream sauce: Bring the heavy cream to a simmer over medium heat and keep simmering until the cream is reduced in volume by about a third., Add the cheese in pieces. Stir until all the cheese melts and the sauce becomes smooth., Toss with pasta and sprinkle servings with pepper and walnuts. Garnish with sage leaves.