Cut it back to a stub about 2 inches tall. When new shoots emerge, select the strongest looking one, and remove all of the rest. Throw some high N fertilizer on it when you cut it back, and water the heck out of it (as appropriate for soil type, weather, etc., you don't want to rot it!). It will grow a nice stalk, and should make a decent head, although never as large as the original one would have been.

Alternatively, if you don't thin the emerging shoots, you will get multiple, small heads.