Loved this, made last night as something a little different for the family! Very straightforward, I did add my carrots with the onion and celery as otherwise they don't seem to soften enough for our taste if added later. I used whole-grain mustard since that was what I had, and I omitted the spinach, personally I love it but the children are not great fans. Since we are not big meat eaters, I used three breasts, cubed them, and cooked them as directed in the recipe, I then added them to the sauce before serving. We loved this rich creamy tangy sauce, which wonderfully complemented the chicken and the accompanying mash (also so good! loved it!) Thank you for a delicious meal, my family are not used to being so spoiled on a weekday night, I know that I'm going to be asked for this again!