Start by adding your mushrooms to a pan with a tiny bit of butter. Saute until the mushrooms have released their water and reduced in size. Keep aside.
In a pot add your butter and oil. Once it's melted, add your crushed garlic and saute until fragrant.
Add flour and mix until the color changes to a very light brown and the flour no longer looks raw.
Take the pot off heat and add your chicken stock slowly, whisking to keep any lumps away.
Add your milk. Whisk.
Add your cream. Whisk.
Put your mixture back on low heat and continue to stir until the sauce begins to thicken.
Once you're close to the consistency you want, add salt, white pepper, garlic powder, paprika, and mixed herbs and stir to combine.
Turn the heat off once your sauce is thick enough for your liking.
Slice or dice your cooked chicken and add it to your sauce along with the cooked mushrooms.
Add your pasta right before serving, sprinkle with cheese.