Return the pan to the heat and add the onion. Cook over moderate heat, stirring, until softened but no browned, about 5 minutes. Add the garlic, ginger, turmeric, honey and cayenne and cook, stirring, until fragrant, about 3 minutes. Add the chicken stock and boil over high heat until reduced by half, about 5 minutes. Add the créme fraîche and cook over moderately high heat, stirring occasionally, until the sauce lightly coats the back of a spoon, about 4 minutes. Season the sauce with kosher salt and black pepper.