This is an incredibly easy and very wonderful way to prepare leeks. It is a perfect accompaniment for grilled fish or chicken served with buttered noodles. From the Perfect Vegetables Cookbook by Cook's Illustrated.
I adopted this recipe from the Recipezaar account. The original poster noted that it is really sweet and good on baked ham. I prepared it for my Easter ham and found it to be sweet with a slight tang from the mustard. I used a powerful, dry, ground mustard and liked the contrast of the bite with the sweetness of the other ingredients.