Bring a large pot of salted water to a boil. Add 8 oz of tagliatelle and cook according to package instructions until al dente, usually about 7-9 minutes. Reserve ½ cup of pasta water before draining the pasta in a colander.
While the pasta cooks, heat 2 tablespoons of olive oil in a large skillet over medium heat. Add 1 cup of sliced mushrooms and sauté for 5-7 minutes until golden and moisture released. Stir in 3 cloves minced garlic and cook for 1-2 minutes until fragrant, being careful not to burn the garlic.
Pour 1 cup of heavy cream into the skillet with mushrooms and garlic. Stir and bring to a gentle simmer. Let the sauce thicken slightly, about 3-4 minutes. Stir in ½ cup freshly grated Parmesan cheese until melted and smooth.
Add the drained tagliatelle to the skillet. Toss gently to coat the pasta in the creamy sauce. Add reserved pasta water as needed to adjust consistency. Season with salt and pepper to taste.
Remove from heat and sprinkle chopped fresh parsley over the top. Serve immediately for best flavor and texture.
