Years ago, I taught for a season in Southwest
England. We lived in an old Anglo-Saxon town -- in
a thatch and cob cottage. It'd stood for 500 years.
Thatch is the thick woven straw that makes the roof.
The walls are a mixture of clay and straw called cob,
or sometimes tabby.

Also from http://www.uh.edu/engines/epi459.htm

i wonder which meaning of cob... i suspect it is related to cobweb, based on an old english word for spiders, coppe, which has totally disappered and leave only cobwebs behind.
(but cobwebs in Websters NW, are any thing flimsy, gausy or ensnaring..

but cob, from the german, *kubb- means anything small, and rounded, and gives use a small lump of coal or corn cobs, and even a short thickset riding horse! but nowhere does it include the meaning you spoke of, dr bill but it is an american dictionary.

cobbler is defined as a clumsy, bungling work man, (and as a repairer of shoes) maybe cob walls are so called because they could be created by even an incompetent person? (unlike fine woodworking)

well, I've certainly cobbled a few things together...

Apple, peach, and blueberry cobblers are all very nice and not especially bungling.