Prep note: Once you begin cooking, this marsala pasta comes together very quickly! I suggest you start by getting all of the chopping, measuring & other prep odds & ends out of the way so cooking is a smooth process: dice the onion, slice the mushrooms, chop the garlic, measure your liquid ingredients, etc. Place everything within an arm’s reach from the stovetop.

1. Boil the pasta: Bring a large pot of water to a boil. Once boiling, generously salt the water. Add the pasta and cook to al dente according to package directions. Reserve 1 cup of the starchy pasta water. Drain the pasta and set aside.
2. Toast the walnuts: Meanwhile, as the pasta boils, toast the walnuts. Add the walnuts to a medium skillet over medium heat. Toast, monitoring closely & shaking occasionally to prevent burning, for 3-4 minutes, just until toasty & fragrant. Transfer toasted walnuts to a plate & set aside. Carefully wipe out the skillet & return to medium heat.
3. Brown the Italian sausage: Add 1 tablespoon of the olive oil to the same skillet used to toast the walnuts in Step 2, increasing the heat to medium-high . Once hot & shimmering, add in the Italian sausage. Cook 5-6 minutes, until browned & rendered, using a wooden spoon to break the sausage into fine bite-sized crumbles as it cooks. If the sausage starts to brown too quickly, reduce the heat to medium or medium-low. Once browned, transfer the sausage to a plate & set aside.
4. Cook the aromatics: If needed, add the remaining 1 tablespoon olive oil to the skillet. Once hot & shimmering, add in the yellow onion & cremini mushrooms. Season with 1 teaspoon kosher salt & ground black pepper, as desired. Cook, stirring occasionally, until the onions & mushrooms soften & begin to caramelize – this will take 8-10 minutes as we’re after nice, browned color. Stir in the garlic & crushed red chili flakes (if using) & cook for an additional minute or so, until fragrant.
5. Build the creamy marsala sauce: Deglaze the pan by slowly pouring in the marsala wine & chicken stock. Use a wooden spoon to scrape up any browned bits that may have formed on the bottom of the pan. Add in the browned sausage & toasted walnuts, stirring to combine. Bring everything to a simmer, then reduce heat to medium or medium-low to maintain a gentle simmer. Stir in the heavy cream & grated parmesan. Cook 3-4 minutes more, stirring occasionally, to allow everything to meld together. At this point, the pasta should be ready to drain.
6. Finish the pasta marsala: Add the pasta to the skillet. Toss to coat with the creamy marsala sauce. Adjust as needed so the marsala sauce evenly coats the pasta – if the mixture is too thick, toss in a little reserved pasta water; if the mixture is too loose, toss in an extra handful of parmesan cheese, etc. Cook over medium heat for 1-2 minutes, allowing the pasta to meld with & absorb some of the sauce. Remove from the heat.  
7. Serve immediately, topped with additional grated parmesan, chopped basil or parsley, &/or a sprinkling of crushed red pepper, as desired. Enjoy!