Cook pasta in a large pot of generously-salted boiling water al dente according to package instructions.  Drain.

Meanwhile, in a separate large sauté pan, add the butter (or olive oil) and cook over medium-high heat until melted.  Add the onion, and sauté for 5 minutes, stirring occasionally, until it is soft and translucent.  Add the garlic and mushrooms and continue cooking for an additional 4-5 minutes, stirring occasionally, until the mushrooms are browned and cooked through.

Slowly pour in the wine, and give everything a good stir, being sure to scrape up any browned bits on the bottom of the pan.  Let the mixture come to a boil and simmer for about 2-3 minutes, or until the wine is reduced by about half.

Add in the crushed tomatoes, rosemary, and crushed red pepper, and gently stir to combine.  Let the mixture continue cooking until it comes to simmer.  Then reduce heat to medium-low, and simmer uncover for about 10 minutes so that the sauce slightly reduces.

Taste, and season with salt and pepper to taste (I added in a generous pinch of each), and also add in extra crushed red pepper if needed.  Remove the sprigs of rosemary and discard.

Once the pasta is cooked and drained, combine it with the mushroom sauce and toss until combined.  Serve immediately, garnished generously with Parmesan (plus chopped parsley or basil, if you’d like).