Winter cress is easy to prepare, and provides a refreshing green flavor in the year's colder months. It is mild, amiable, unthreatening, and very good for you.
I took a simple approach to cooking the small bunch that I imported from Kentucky to New York (see previous entry for an account of the massive carbon-eating travels of two small plants): Boil briefly to remove bitterness. Cut it up a bit and saute in (olive) oil with salt and pepper. For about two minutes. Serve as a side dish or in a stir-fry. Add in garlic as desired.
In other words, it's a widely-available-for-the-picking midwinter substitute for spinach and other greens. Euell Gibbons ("Stalking the Wild Asparagus," McKay, 1973) says there are two main forms of this mustard family member. They look just about the same and between them can be found in low wet areas and in fallow fields. Gather the leaves in winter or in very early spring -- later on the leaves are bitter.
One warning: as with all wild food gathering, be careful of environmental problems with the gathering site. For example, I found winter cress in abundance down by Cayuga Lake in early spring, thriving under heavy foot traffic -- on a dog walk trail, next to an industrial site. Leave those alone, as with any plants growing in or near still or flowing water that might be polluted. No, that does not rule out every plant....not quite.