Once the butter is melted place in the onions and mushrooms and cook for 8-10 minutes until browned and tender. All the moisture from the mushrooms will secrete and then go back in.
Stir in the garlic and cook for 20 to 30 seconds and then sprinkle in the flour and mix. Next, deglaze with the sherry wine which will immediately absorb into the mushrooms and onions.
Pour in the chicken stock and stir to mix. Bring the mixture to a boil. Once boiling it should be very thick and at this point pour in the cream to and mix to form a creamed mushroom sauce.
Add in the turkey, ½ cup of parmesan cheese, salt and pepper and mix to combine. Set aside and keep warm. In a large pot of boiling salted water add in the pasta and cook until al dente.