Preheat the oven to 350 degrees Fahrenheit (176 Celsius).
Cook pasta until al dente per the instructions on the package.
While the pasta is cooking, melt two tablespoons of butter into a large skillet and cook the mushrooms until they are dark in color (around 6-8 minutes).
Melt a stick of butter on medium heat in the same pan that you cooked the mushrooms. Once the butter is melted, add the flour to the butter and stir into a rue. Cook until the rue turns a light brown (around 5 minutes), making sure you stir continuously so it doesn't burn.
Once the rue is brown, add the turkey (or chicken) broth and half and half. Increase the heat to medium high, stirring frequently so the cream doesn't burn. As you stir, make sure to scrape any bits from the bottom of the pan as this will add flavor.
Once the sauce comes to a simmer, reduce heat to low and stir for a few minutes until the sauce is thickened.
Add mushrooms back to the pan along with the turkey, parmesan cheese, nutmeg, white pepper, and salt. Stir until everything is combined and the cheese is melted.
Add the pasta to a greased casserole dish and pour the sauce over the pasta. Gently combine with a fork.
Bake uncovered at 350 degrees Farenheit (176 Celsius) for 30 minutes.
Serve and enjoy!