Wash the sorrel leaves well and spin dry in a salad spinner. Melt the butter in an ovenproof casserole. Add the garlic and sorrel and cook until wilted, about 5 minutes. Drain off any excess water. In a small bowl whisk together the yolks and crÅme fraöche. Season with salt and pepper. Pour the cream mixture into the sorrel and place over an extremely low heat. Stir constantly until thickened, but do not allow to boil.
