It's a Caryopteris, probably Caryopteris x clandonensis, though I've not heard of that plant having culinary uses. The bloom structure of Centaurea dealbata is different, and it blooms earlier in the summer.

Other images of caryopteris are at http://www.google.com/images?q=caryopteris+x+clandonensis&hl=en&client=firefox-a&hs=pDK&tbo=1&rls=org.mozilla:en-US:official&prmd=i&source=lnms&tbs=isch:1&ei=qn2HTJXPAsWclges5OWYDg&sa=X&oi=mode_link&ct=mode&ved=0CB4Q_AU&biw=1440&bih=733

Thanks drbabs. I've not eaten any of them which I have even the slightest doubts about since my investigations began!

KB, I'm looking on all sorts of plant sites for you and I think it's a perennial flowering plant called CENTAUREA DEALBATA (PERSIAN CORNFLOWER). Sure is pretty! I don't think it's edible, though. CHeck this out:

http://davesgarden.com/guides/pf/showimage/126531/