Season chicken well.
Heat 1 tablespoon of butter in 12-15 inch large saucepan over medium heat. Season chicken with salt and pepper, and cook until juicer are clear and exterior is nicely browned. Once chicken has cooked through, set aside.
Add remaining tablespoon of butter and cook the Portobello mushrooms until softened. Set aside with chicken.
Add chicken stock, milk, and minced garlic. Bring just to a simmer over high heat.
Reduce heat to medium, add pasta directly to pan, do not crack in half.
Stir pasta with tongs every few minutes to prevent sticking. Replace lid after stirring each time. If at any point, your pasta is not mostly covered in liquid, add additional chicken stock and/or milk. Cook for about 10 minutes (pasta will not be fully cooked).
Add heavy cream, parmesan cheese, and plenty of fresh cracked pepper (to taste), and additional salt if desired.
Simmer until sauce is just thickened and pasta is cooked (sauce will continue to reduce as it stands, so pull a bit before you think you should).
Slice chicken and add chicken and mushrooms to the pan.
Serve with plenty of freshly grated parmesan, parsley, basil and more pepper if desired.
Note: In one pan pastas, liquid needs can vary drastically depending on the size of pan you have to use and your stove’s exact heat temperature. A smaller pan will require less liquid as it boils and evaporates slower. Your pasta should always be mostly (if not fully) covered in sauce or it will not cook through. Adjust as needed and thin sauce with additional stock or milk if needed to keep pasta submerged.