Heat pasta water and cook according to directions, while the sauce is being prepared.
Melt butter and olive oil over medium high heat.
Salt and pepper the chicken and add it to skillet. Brown well on one side, then turn for a total of about 7 minutes or until chicken is cooked through. Remove and place in a bowl.
Add onions and mushroom and sprinkle with salt and pepper. Cook until onions are tender and mushrooms are starting to brown - about 3 minutes. Remove from the pan and add to the bowl with the chicken.
Pour the sherry in the pan and scrape up any brown bits. Pinch the cream cheese into small pieces and add it and the broth to the skillet. Simmer for about 3 minutes, breaking up the cream cheese. It will not completely melt.
Add the chicken mixture and the pasta to the skillet. Toss to coat, taste and add salt and pepper if needed. Optionally garnish with parsley.
Note - you can easily make this your own - use different mushrooms or a variety. Add garlic or peppers. Sun dried tomatoes would also be good.