A young cabbage head, in a garden in rural Mecklenburg County, North Carolina, USA. It has probably been cut off and eaten by now. I don't know what the yellow stuff is on the left extending furthest to the left. Note that this garden is almost weed-free!
Cabbage heads are mostly leaves, wrapped around each other. Cabbage is a member of the Mustard family, as are broccoli, radishes, mustard, and other edible plants. I guess we eat every part of some member of the mustard family.
More detail can be seen at the larger sizes.