Chicken with Mustard Mascarpone Marsala

This is a recipe from Giada that I got off the internet. I made it once for my friend Alicia, who does not like mushrooms, and so I substituted fresh spinach instead. It was so good, that now I add spinach every time!

4 boneless skinless chicken breasts
Salt & pepper
2 Tbsp. olive oil
5 Tbsp. butter (divided)
¾ c. onion, chopped
1 lb. cremini mushrooms
2 Tbsp. garlic
1 c. dry Marsala
1 c. (8 oz.) mascarpone cheese
2 Tbsp. dijon mustard
2 Tbsp. parsley
12 oz. fettuccine (or preferred pasta - we use farfalle)
fresh spinach (optional)

Cut chicken into bite-size pieces. Sprinkle with salt & pepper, cook in olive oil over med-high heat, and then set aside when done. While chicken cools, melt 2 Tbsp. butter over med-high heat and add onion (2 min.) then mushrooms and garlic (12 min.), then add wine and simmer (4 min.), then stir in mascarpone and mustard, return chicken to pan for 2 minutes and season with salt & pepper. (If using fresh spinach, add at the very end before serving). Serve with pasta.