- Sprinkle the chicken with salt and pepper. Heat the oil in a heavy large skillet over high heat. Add the chicken and cook just until brown, about 4 minutes per side. Transfer the chicken to a plate and cool slightly.
- While the chicken cools, melt 2 tablespoons of butter to the same skillet over medium-high heat, then add the onion and saute` until tender, about 2 minutes.
- Add the mushrooms and garlic and saute` until the mushrooms are tender and the juices evaporate, about 12 minutes.
- Add the wine and simmer until it is reduced by half, about 4 minutes. Stir in the mascarpone and mustard. Cut the chicken breasts crosswise into 1/3-inch-thick slices.
- Return the chicken and any accumulated juices to the skillet. Simmer, uncovered, over medium-low heat until the chicken is just cooked through and the sauce thickens slightly, about 2 minutes. Stir in the chopped parsley. Season the sauce, to taste, with salt and pepper.
- Meanwhile, bring a large pot of salted water to a boil. Add the fettuccine and cook until al dente, stirring occasionally, about 8 minutes. Drain. Toss the fettuccine with 3 tablespoons of butter and season, to taste, with salt and pepper. Swirl the fettuccine onto serving plates. Spoon the chicken mixture over top.
- Garnish with parsley sprigs and serve.
I use mushrooms that are available in my area.