Bring cold salted water to a boil for the pasta. While it's coming to temperature, melt the butter in your large sauté pan over medium heat. Once the butter is melted, add the sliced mushrooms into the pan along with about half of the truffle spread. Sprinkle with about ½ teaspoon salt, stir occasionally and let the mushrooms cook through for 6-7 minutes.
3 tablespoon butter, 8 ounces cremini mushrooms, 3 tablespoon truffle spread
At the seven minute mark, add the minced garlic and fresh thyme to the hot pan of sliced mushrooms and stir so the garlic doesn't burn. Cook for a minute, until the garlic becomes very fragrant. (If the water is boiling now, add your dried pasta in!)
2 garlic cloves, 1 teaspoon fresh thyme, 4 ounces fettuccine pasta
Pour the heavy cream into your pan of mushrooms and add the other half of truffle spread. Stir together well and let simmer on medium heat, stirring occasionally, for 8-10 minutes until the heavy cream reduces by about half. Once it's reduced, add the juice of half a lemon, give a taste and add more if more acidity is needed. Don't worry about the salt just yet, the parmesan in the next step is also salty.
3 tablespoon truffle spread, ¾ cup heavy cream, 1 lemon
Turn the heat off under the mushroom pan and stir in the parmesan cheese in three batches, stirring until each batch is smooth in the sauce.
½ cup parmesan cheese
Add the cooked pasta and the truffle butter to the sauce, using tongs to toss the pasta and coat the noodles well with the creamy mushroom sauce. Taste the dish again and add salt and pepper to taste if needed, then toss the noodles again to incorporate any added seasoning.
2 tablespoon truffle butter, kosher salt and freshly ground pepper
Serve immediately with grated lemon zest, parmesan cheese, and chopped fresh parsley on top of the pasta.
2 tablespoon fresh parsley, 1 lemon, 2 tablespoon parmesan cheese