Fill a large pot with water, adding a generous pinch of salt, and bring it to a rolling boil over high heat. Once boiling, add the spaghetti and cook according to package instructions, usually 8-10 minutes, until al dente. Reserve about a cup of pasta water, then drain the rest.

In a large skillet, heat a tablespoon of olive oil and two tablespoons of butter over medium heat. Once the butter melts and begins to foam, add the sliced fresh mushrooms. Cook for about 5-7 minutes, stirring occasionally, until golden brown.

Lower the heat to medium-low and add minced garlic to the skillet with the mushrooms. Sauté for an additional 2-3 minutes, allowing the garlic to soften without burning.

Add the drained spaghetti directly into the skillet with the mushroom-garlic mixture. Pour in a bit of reserved pasta water, stirring gently to combine everything evenly. Cook for about 2 minutes, ensuring the pasta is well-coated.

Remove the skillet from heat and stir in the remaining butter and freshly grated Parmesan cheese, mixing until creamy. Toss in chopped fresh parsley for color and flavor.