Dust chicken breasts with flour and brown, skin side down, in butter in large skillet. When skin is brown and crisp, turn and cook other side until barely done, about 10 minutes in all.
Remove pan from heat. Pour brandy over chicken and ignite. When flames die down, remove chicken to platter and keep warm in a low oven.
Add garlic and shallots to pan and sauté briefly. Add sliced mushrooms and sauté 3 minutes. Add cream, mustard, and parsley. Cook over high heat, stirring continuously, until reduced and thickened. Season to taste with salt and serve over chicken.