Lightly season the chicken breasts with salt and pepper.
In a large skillet over medium heat, brown chicken breasts on both sides.
Add onions and mushrooms and stir cook until the onions soften.
Transfer mixture to a shallow casserole dish and bake, uncovered, for 15 minutes.
In a small sauce pan warm the orange liqueur over low heat (should be lukewarm, not hot). Take the casserole out of the oven.
Pour the liqueur over the chicken and vegetables and ignite it. When the flames die out, add the wine and return the casserole to the oven for another 15 minutes or until chicken breasts are no longer pink inside. Remove the casserole from the oven.
Arrange the chicken and vegetables on a warm platter and keep hot. Mix butter and flour to make a paste. Stir this into the pan juices, add cream and simmer over low heat for 5 minutes until thickened.