In a large food processor, blend flour, eggs, egg yolks and salt until a homogenous dough forms. Tip onto a clean bench, then knead the dough until completely smooth and elastic, 5-10 minutes. Cover the dough tightly and rest at room temperature for 30 minutes. Don’t worry if the dough seems too firm and dry at this stage - it will soften as it rests.
Divide rested dough into 4 even portions. Work one portion at a time, keeping the other portions covered. Use a pasta machine to roll the pasta to 1.5mm thick (that’s position 5 on a Marcato Atlas 150). Cut the pasta sheet in half. Arrange sage leaves over one sheet, then place the second sheet on top. Flatten gently with a rolling pin, then trim the edges with a knife. Feed through the pasta machine again, rolling to 1mm thick (position 6). Cut rolled pasta into 12” sheets, then hang on a drying rack (or similar - be creative) to air dry for approximately 1 hour. Repeat with remaining pasta. Roll the dried pasta sheets through a fettuccine attachment. Alternatively, cut by hand a ¼ inch thick. Portion into 6 even bundles (about 4oz each) and store in an airtight container. The fettuccine will keep in your fridge for 1 week, or in the freezer for 1 month.
FOR THE SAUCE
Bring a pot of salted water to a heavy boil. Add two portions of fettuccine and cook until al dente, about 90 seconds. Strain, reserving ⅔ cup of the cooking water. Place a sauté pan over high heat. Bring White Truffle Oil and the reserved pasta water to a simmer, then add the fettuccine and butter, plus salt and pepper to taste. Toss vigorously until a silky sauce forms. Serve garnished with lots of freshly grated parmesan cheese and shaved truffles, if using.