Cook the pasta according to package instructions until al dente. Reserve 1/2 cup of the pasta water, then drain and set aside.

In a large skillet, heat olive oil and butter over medium heat. Add the minced garlic and sauté for 1-2 minutes until fragrant.

Add the sliced mushrooms to the skillet and cook for 5-7 minutes, stirring occasionally, until the mushrooms are tender and golden brown.

Add the spinach to the skillet and cook for 2-3 minutes, stirring, until wilted.

Pour the heavy cream into the skillet and stir to combine. Reduce the heat to low and let it simmer for 2 minutes.

Add the grated Parmesan cheese, red pepper flakes (if using), and reserved pasta water. Stir until the sauce is creamy and smooth.

Season the sauce with salt and black pepper to taste.

Add the cooked pasta to the skillet and toss until evenly coated with the sauce.

Serve immediately, garnished with fresh parsley if desired.