Cook the pasta according to package instructions in a large pot of salted boiling water until al dente. Drain and set aside, reserving 1/2 cup of pasta water.

In a large skillet, heat olive oil and butter over medium heat until melted.

Add the minced garlic and sauté for about 30 seconds until fragrant.

Add the sliced mushrooms to the skillet and cook for 5-7 minutes, stirring occasionally, until the mushrooms release their moisture and become golden brown.

Stir in the fresh spinach and cook for 2-3 minutes, until wilted.

Reduce the heat to low and pour in the heavy cream, stirring to combine. Allow the sauce to simmer for 2 minutes.

Add the grated Parmesan cheese and stir until melted and the sauce thickens slightly. If the sauce is too thick, stir in the reserved pasta water a little at a time until desired consistency is reached.

Season the sauce with salt, black pepper, and crushed red pepper flakes (if using), to taste.

Add the cooked pasta to the skillet and toss to coat evenly in the sauce.

Serve immediately, garnished with additional Parmesan cheese if desired.