Step 1Melt the butter in a medium saucepan over medium-low heat. Add the cream and one-eighth teaspoon salt and bring to a low simmer. Remove the sauce from the heat and shave 1 truffle onto the surface. Stir to combine, then set the sauce aside to allow the truffle flavor to infuse.
Step 2Combine the egg yolks and olive oil in a bowl, stirring to mix.
Step 3Measure the flour, pepper and remaining one-half teaspoon salt onto a clean work surface and stir to combine. Make a well in the center of the flour and slowly pour in the egg mixture. Use a fork to stir the flour into the egg mixture, then, as the dough forms, use your hands to bring it together into a ball. Add the water one tablespoon at a time as needed.
Step 4Knead the pasta dough for 5 to 7 minutes until it becomes soft and smooth. Form it into a ball and wrap in plastic wrap. Set aside to rest for one-half hour.
Step 5Divide the pasta dough into 8 pieces. Using the widest setting on the pasta machine, put 1 piece of dough through once. Fold the short ends of the rectangle into the center (making 3 layers) and put it through twice more on that setting. Then change to the next-widest setting and run the dough through once. Change to the next setting down and run the dough through again. Continue the process twice more, changing to narrower settings each time, for a total of 5 settings. Set each pasta sheet aside and cover it with plastic wrap and continue with the remaining dough pieces.
Step 6Change the attachment on the pasta machine to the fettuccine-cutter and run each sheet of pasta through. Place the noodles on a clean surface.
Step 7Bring the cream sauce to a simmer over low heat. Simmer gently until slightly thickened, about 20 minutes.
Step 8Meanwhile, bring a large pot of salted water to a boil. When the cream sauce is ready, add the fettuccine to the boiling water and cook until slightly firm but tender, about 2 minutes. Drain.
Step 9Combine the pasta and sauce in a large, warmed serving bowl. Toss with tongs to coat each pasta strand. Using the truffle shaver, shave the remaining truffle over the top and serve.