Gather the ingredients.

Fill a large pot with lightly salted water and bring to a rolling boil. Cook fettuccine at a boil until tender yet firm to the bite, about 8 minutes. Drain but do not rinse pasta; transfer to a large serving bowl and keep warm.

Meanwhile, heat olive oil in a large skillet over medium heat. Cook and stir white and shiitake mushrooms in hot oil with a pinch of salt until liquid from mushrooms evaporates and mushrooms are browned, about 10 minutes.

Stir garlic into mushrooms and cook for 1 minute; pour in sherry and cook until wine is nearly evaporated. Stir in chicken stock; season with salt and black pepper. Bring to a simmer, reduce heat, and cook until slightly thickened, about 5 minutes.

Pour cream into mushroom mixture, stir to combine, and simmer for 5 minutes. Mixture will foam and thicken slightly.

Stir thyme, chives, and tarragon into mushroom sauce and turn off heat; mix 1/2 cup Parmigiano-Reggiano cheese into sauce until cheese is melted.