Mustard - A combination of stone ground mustard (which contains whole seeds) and smoother Dijon mustard gives this dish great flavor and texture. If you only have one type of mustard, you can absolutely still make the recipe, but start with just 1 tablespoon total (instead of 4 teaspoon of two types as listed in the recipe) of mustard. You can always stir in more mustard to the sauce after you taste it. Dijon mustard has a sharp, slightly spicy flavor, so feel free to reduce the amount of Dijon if you’d like a more mild mustard flavor.
Creme Fraiche - Creme Fraiche is a creamy, sour dairy product that is similar to sour cream but has a much thicker texture. Look for it in the dairy section, often near other soft, specialty cheeses (like ricotta, mascarpone, or perhaps near the goat cheese and fresh mozzarella). If you can’t find creme fraiche, you can make this recipe with sour cream, but do not cook the sour cream over direct heat (it may separate). After whisking in the wine, stock, mustard, and lemon juice and cooking the sauce down to your desired consistency, take the pan off the heat and whisk in sour cream. Then add chicken and parsley to finish.