Cook Pasta: Bring a large pot of salted water to a rolling boil. Add the pasta and cook according to package directions until al dente. Reserve about 1 cup of the pasta cooking water before draining. Drain the pasta and set aside.

Sauté Mushrooms: While pasta cooks, heat 1 tablespoon of olive oil in a large skillet or Dutch oven over medium-high heat. Add the sliced mushrooms in a single layer (cook in batches if necessary to avoid overcrowding, which steams rather than browns them). Cook for 5-7 minutes, stirring occasionally, until the mushrooms are golden brown and have released their moisture.

Add Aromatics & Spinach: Reduce heat to medium. Add 1 tablespoon more olive oil (or a tablespoon of butter) to the skillet, if needed. Add the minced garlic and cook for 1 minute until fragrant, being careful not to burn it. Add the fresh spinach in batches if necessary; it will wilt down quickly. Cook until all the spinach is wilted, about 2-3 minutes.

Create Sauce: Pour in the vegetable broth (or chicken broth). Bring to a gentle simmer. If using, add a pinch of red pepper flakes now. If you want a creamier sauce, stir in 2-3 tablespoons of cream cheese or a splash of heavy cream until melted and smooth.

Combine Pasta: Add the cooked and drained pasta to the skillet with the sauce and vegetables. Toss everything together, coating the pasta evenly.

Adjust Consistency & Season: If the sauce seems too thick, add a splash or two of the reserved pasta cooking water until it reaches your desired consistency. Stir in half of the grated Parmesan cheese (if using).

Serve: Taste and season with salt and black pepper as needed. Serve immediately, garnished with remaining Parmesan cheese and a squeeze of fresh lemon juice, if desired.