Bring a large pot of salted water to a boil. Add your penne pasta and cook according to package instructions until al dente. Drain and set aside. You may want to toss it with a touch of olive oil to prevent sticking.

While the pasta cooks, season the chicken breasts with salt and pepper. Heat 1 tablespoon of unsalted butter in a large skillet over medium-high heat. Add the chicken and cook for about 6-7 minutes on each side or until golden brown and cooked through. Remove from the skillet and let it rest before slicing into bite-sized pieces.

In the same skillet, add the minced garlic, sliced shiitake mushrooms, and diced red onion. Sauté for about 5-7 minutes until the vegetables are soft and the mushrooms release their moisture. This step intensifies the flavor dramatically.

Pour in the Madeira wine (or Marsala wine) to deglaze the skillet. Scrape any bits stuck to the bottom. Let it simmer for about 2 minutes until reduced slightly. Then, add the chicken broth, heavy cream, sour cream, and Dijon mustard (if using). Stir until everything is well-combined and simmer for another 5 minutes.

Add the cooked chicken and pasta to the skillet. Toss everything in the sauce until well-coated. If necessary, season with additional salt and pepper to taste.

Once everything is combined, remove from heat. Garnish with fresh parsley and sprinkle with freshly grated Parmesan cheese. Serve immediately and enjoy every bite!