Heat 2 Tbsps butter in a large deep sided pan. Brown the chicken breasts on all sides over medium high heat. About 3-4 minutes total. Remove breasts to a platter.
Reduce the heat to medium and melt remaining 2 Tbsps butter in the pan. Add the onions and cook about 5 minutes. Add the mushrooms and cook for another 3-4 minutes. Add the garlic and cook another minutes.
Remove the sliced onion pieces and reserve for garnish of the finished dish.
Remove the pan from the heat and stir in the flour so the vegetables are coated and the flour is moistened.
Return the pan to the heat and add the chicken back into the pan.
Add the natural apple cider, chicken stock, brandy, hard cider and pepper. Cover and cook over medium low about 20 minutes until chicken is cooked through.
When the chicken is cooked add ¾ cup of cream and the salt.
Measure the corn starch into a small dish and stir in the remaining ¼ cup of cream until corn starch is dissolved.
Add the cornstarch mixture to the chicken dish and stir until sauce thickens.
Serve over pasta or with mashed potatoes.