For the Gnocchi:
Bring a large pot of salted water to a boil. In a large mixing bowl, combine both cheeses, olive oil, and eggs and season generously with salt and pepper. Combine with a whisk, then add the flour in 3 batches, stirring with a rubber spatula until the dough just comes together. Turn out onto a floured surface and divide into 4 pieces. Roll each piece into a dowel shape about 5/8” in diameter, then cut into 5/8” long pieces. Transfer to a sheet tray dusted with some flour while you finish rolling all the dough. Once the gnocchi are all rolled and cut, cook in the boiling water for about 2 minutes, or until it floats to the top. Reserve 1 cup of the cooking liquid, then drain the gnocchi and shock it in ice water to stop cooking. Drain completely, then toss with olive oil and lay on a flat tray. Allow the gnocchi to dry on a flat tray in the refrigerator for 2 hours. This can be done up to 3 days in advance; just store the gnocchi in a covered container in the refrigerator until it is ready to use.
To Finish:
Set a large, preferably non-stick pan over medium heat. Add a drizzle of olive oil and the gnocchi and sauté until golden brown. Add the mushrooms and continue to cook until heated through. Add truffle butter and ½ cup of the reserved pasta cooking liquid and bring to a simmer, continuing to swirl the pan to emulsify the sauce. Cook until the gnocchi are coated in a velvety, buttery sauce. Remove from heat, season with salt and pepper, and toss with fresh minced chives. Plate and serve immediately, with more grated parmesan cheese on the side.
