Slice the mushrooms. I prefer to remove the stems first.
Put the flour and 1/2 tsp of salt into a plastic bag
Add chicken to bag and shake to coat chicken well.
Heat the olive oil and 1 tbsp butter in a skillet over medium high heat. Not hot enough to burn the butter!
Add the chicken to the pan and cook about 5-6 minutes per side until the flour turns golden brown and the middle of the chicken reaches 145 degrees F. Remove the chicken to a plate and cover with foil
Turn the heat down to medium and add the rest of the butter and saute the mushrooms for 4-5 minutes. Add the shallots and garlic and cook for a minute more
Add the Marsala wine, cream, and chicken stock to the pan. Raise the heat long enough to bring it to a boil and then lower the heat and simmer stirring occasionally until it is reduced by about half.
Add salt and pepper to taste
Add the chicken back into the pan, cover, and let it simmer while you cook the pasta
Fill a large skillet with cold water. Lay the spaghetti in the bottom of the pan and add salt. Turn the heat on high. Once the water starts to boil, set a timer for 6 minutes. The pasta should be al dente after the timer. Cook an additional minute or two if necessary.
Serve the chicken over the pasta and cover with mushrooms and sauce.