Preheat the oven to 400F. Butter a roasting pan and place the sole fillets in the pan. Season with salt and pepper. Place the apple slices on the fish fillets and pour in the apple juice or cider. Bake for 10 minutes. Transfer the sole and apple slices to a warmed serving platter and keep warm. Pour the cooking liquid into a small saucepan and boil hard until reduced to 1/2 cup. Add the crÅme fraöche to the saucepan and bring to a boil. Remove the pan from the heat and whisk in the butter, a little at a time. Do not boil the sauce. Spoon the sauce over the sole before serving or serve it separately.
