Cook the Pasta to Al Dente: Bring a large pot of salted water to a boil. Add the pasta and cook according to the package instructions until al dente. Reserve a small cup of pasta water (optional), then drain and set the pasta aside.
Sauté the Mushrooms and Garlic: While the pasta cooks, heat the butter and olive oil in a large skillet over medium-high heat. Add the sliced mushrooms and garlic, stirring often. Cook for 5–6 minutes, or until the mushrooms have released their moisture and the liquid has mostly evaporated.
Prepare the Creamy Sauce Base: Transfer the mushrooms to a plate and return the pan to the heat. Pour in the white wine and stir in the Italian seasoning, lemon juice, flour, and Dijon mustard. Whisk gently to create a smooth, fragrant base.
Simmer the Cream Sauce: Reduce the heat to medium and slowly add the heavy cream to the pan. Stir well and let the sauce simmer for 2–3 minutes, allowing it to thicken slightly.
Combine Mushrooms and Sauce: Return the sautéed mushrooms to the pan and stir to coat them in the sauce. Let everything cook together for a few more minutes until the sauce reaches your desired thickness. Season generously with salt and freshly ground pepper to taste.
Toss Pasta and Finish the Dish: Add the drained pasta to the skillet and toss until evenly coated in the sauce. If needed, add a splash of reserved pasta water to loosen the sauce. Stir in chopped parsley and top with freshly grated parmesan, if using.