"Once upon a time, there was an Italian farmer and his wife who was waiting for her dear husband to return from the field. She made some pasta and poured some wine. The beloved husband returned and ate his pasta and drank his wine. He kissed his wife and said 'Amore! Your food is delicious as always. But I am a bit tired of pasta.' 'Don't you worry, my dear husband,' the wife replied, 'Tomorrow you will have something different.
Preheat the oven to 450 degrees F (230 degrees C).
Prick russet potato and sweet potato all over with a fork. Wrap individually in aluminum foil.
Bake in the preheated oven until soft, about 1 hour 15 minutes. Unwrap the potatoes and let cool slightly.
Remove skin from the potatoes and mash flesh in a bowl. Let cool, at least 15 minutes. Add egg and mix with a fork. Mix in all-purpose flour gradually using a spoon; knead together by hand as dough becomes tougher.
Dust your work surface with rice flour. Place the dough on the surface; it will be quite sticky. Cut into 8 pieces; place on a tray and freeze until easier to handle, about 10 minutes.
Take 1 piece of dough from the freezer. Roll out into a long sausage on the dusted work surface. Cut into comparably small gnocchi pieces, the smaller the better. Transfer to a dish covered with plastic wrap and dusted with flour. Repeat with the remaining 7 pieces of dough. Transfer gnocchi to the freezer until ready to cook.
Bring a large pot of lightly salted water to a boil. Cook gnocchi in the boiling water until they float to the top, 3 to 4 minutes.
Combine olive oil, butter, sage, and garlic in a large saucepan over medium-low heat. Cook and stir until butter is melted and flavors are combined, 2 to 3 minutes. Remove garlic and add the gnocchi. Top with Parmesan cheese and mix well.