Boil a large pot of water and cook your fettuccine pasta as directed on the package, or until al dente. Reserve a cup of the cooked pasta water. Strain the pasta and reserve.
While the pasta is cooking, prepare chicken and the sauce.
Place the cubes of raw chicken in a large bowl. Sprinkle the ¼ cup of flour on the chicken and toss everything to coat.
Drizzle the olive oil in a large non-stick skillet over medium-high heat. Place the coated chicken in the skillet. Once fully cooked and golden on all sides, remove from the pan and place in a clean bowl.
Deglaze the skillet by slowly pouring in ½ cup of the chicken broth. Scrape up any stuck on bits from the bottom. Add the slices shallot and garlic into the skillet and cook for 2 minutes.
Add the Mushrooms to the pan with the salt and cook until the mushrooms have reduced and are nice and golden. Deglaze the pan again with the other ½ cup of chicken broth.
Add the heavy cream and Marsala wine to the pan. Bring to a simmer and add the tarragon, chives, and Dijon mustard. Stir to combine.
In a small bowl, combine the 1 tablespoon of flour with about 2-3 tablespoons of the sauce from the skillet. Mix until smooth and pour back into the skillet. Stir until sauce has thickened.
Add the cooked chicken cubes back into the sauce. You can combine the cooked pasta with the sauce before serving, or ladle the sauce over the pasta on the plates. Garnish with fresh parsley and grated parmesan cheese. Enjoy!