This foot-wide spreading groundcovery clump of foliage is an edible herb,
but which one:

http://www.paghat.com/images/tasty_apr.jpg

The woman I got it from said it's "variegated cress" but I can't find a
garden cress species with such ornate serated leaves. It has an almost
peppery taste.

Well, there IS a variegated cress -- Barbarea vulgaris 'Variegata', commonly
known as Winter Cress or Yellow Rocket. I was looking at some photos on the
'net and they all showed the leaves fringed by a white/pale color.

James