cannonball = "bread bowl"

Today I got an e-mail invitation to a pot-luck dinner. It included the information that "this week's theme will be cannonballs." At a loss, I asked the host what he meant by this, and I got this explanation:

Cannonballs are bread that you scoop out and you eat something out of them like chili, clam chowder, stew, etc. They are used instead of bowls.

I must admit, I've always just called those "bread bowls."

Now, this dinner is taking place here in Seattle, a place I haven't lived very long. After a little online searching, it became clear that this is a Pacific Northwest regional term. In fact, it seems more rooted in western Oregon than here in the Puget Sound area; every online example whose origin I could verify was from Oregon. I can find no documentation of this term anywhere, not even in regional slang dictionaries or food dictionaries, or on websites devoted to slang such as Grant Barrett's doubletongued.org or the American Dialect Society's listserve archives.

Here are some citations:

• "Mo's bacony chowder is so thick that it actually rises higher than the edges of the bowl in which it's served, unless you get the Cannonball, which is a bread bowl filled with it." —Jane and Michael Stern, 500 Things to Eat Before It's Too Late, 2009 (review of Mo's West, a chowder house in Otter Rock, OR)
• "Cannonballs- bread bowls baked with garlic butter and filled with your choice of..." — Laurelthirst Public House menu, Portland, OR
• "Jumpstart the party with your choice of zippy dips! Served inside our sourdough cannonball bread with an assortment of breads and crackers." — Zupan's Delimenu, Portland, OR
• "1 Medium sized cannon ball bread" — "Brie Fondue" recipe, Coast To the Cascades decorative painting society, Springfield, OR
• "Chili or Clam Chowder served in a “cannon ball” bread bowl is also quite popular." — Davidson's Casual Dining, Tigard, OR

• Is anyone else familiar with this term? Have you heard it used outside of Oregon?