01 - Boil water with salt in a large pot. Add pasta and cook according to package instructions until al dente. Reserve 1/2 cup pasta water, drain and set aside.
02 - Heat olive oil in a large skillet over medium heat. Add chopped onion and sauté for 2 to 3 minutes until softened.
03 - Add minced garlic and sliced mushrooms to the skillet. Cook 6 to 8 minutes, stirring occasionally, until mushrooms are golden and moisture evaporates.
04 - Stir in fresh spinach and cook for 1 to 2 minutes until wilted.
05 - Reduce heat to low. Pour in heavy cream and vegetable broth, then add thyme, ground black pepper, and salt. Simmer gently for 2 to 3 minutes.
06 - Add grated Parmesan cheese and stir until melted and sauce is smooth. If the sauce is too thick, gradually add reserved pasta water to adjust consistency.
07 - Add cooked pasta to the skillet, tossing to coat evenly with the sauce. Heat for 1 to 2 minutes, adjusting seasoning as needed.
08 - Plate immediately. Garnish with extra grated Parmesan cheese and freshly ground black pepper.