Hi, Sara and David,
Thanks for giving me so much to think about. It's funny: I've never considered the definition of a cookie; I always figured I'd know one when I saw one. And since I love cookies immoderately, I say three cheers for Anita Chu for casting the net wide and including treats like profiteroles (little cream puffs filled with ice cream) and those Algerian almond tarts in her wonderful new Field Guide to Cookies. Of course, she couldn't get away with that in France, where a pastry chef's taxonomy of sweets is so precise: Profiteroles are classified as dessert, tarts are pastries, and bunches more of her sweets wouldn't qualify as cookies (which the French call gateaux secs), either.
Fun probably wouldn't be part of a scholarly definition of the cookie in any country, but I think one reason cookies are such a beloved part of the American culinary tradition is that you eat them with your fingers. They are, as both of you said, handheld or portable—when you've got to grab a fork to munch on a sweet, I think you've left cookiedom—and what's better than playing with your food?
David mentioned that you should be able to polish off a cookie in three bites. I'd add that cookies shouldn't be more than a bite larger. I really dislike what Sara calls "monster cookies." And don't get me started about those cookies that tip the scales at about 6 ounces and are almost raw in the center. In a perfect cookie world, cookies would be 3 inches around, crisp close to the edges, and just a little chewy in the center (just the way you like them, Sara). And they'd be fully baked. Again, not really a defining characteristic, but one I think makes a huge difference in the taste department—when you bake a cookie until it's truly golden, you get great caramel flavor from both the sugar and the butter. Cookies in this baker's paradise would not, however, have to be round! Sorry, David (even if you did only just make the point up). Limit cookies to roundness, and you miss out on bar cookies, like brownies—and my guess is that none of us would want to miss out on those!
Finally, I'm with you both on chunkiness and "sedimentary matter"—as Sara so adorably called mix-ins like chips and nuts—being a big part of what makes a cookie all-American. Maybe it's because, as you said, we Americans like to customize everything (David, I giggled when you wrote about how everyone wants to make changes in restaurant dishes), but I think it comes back to fun and, for me, surprise. When you've got lots of stuff in a cookie, it means that no two bites will be the same—some will have more chips, some more nuts, some a raisin, some a bit of brickle—and that you'll be surprised from first taste to last. I think it's part of what keeps us coming back for more.
Of course, coming back for more has never been an issue for me, and while my favorite cookies are crisp and crunchy and chockablock with mix-ins, I've got soft spots in my heart for lots of different kinds of cookies. I'd be happy to have Sara's spurned shortbreads and sugar crisps, which I love for their simplicity and luxurious butteriness. I could go through a box of Mallomars, one of David's favorites, any day and would eat them just the way I did as a child: First, I'd poke a hole in the chocolate covering the marshmallow, then I'd nibble away at the chocolate until the marshmallow sat naked on the graham cracker and I'd be able to pop the marshmallow into my mouth, whole, and chase it with the cracker. I'm always content when there are madeleines (really cookie-size cakes), Linzer cookies (spice cookies sandwiched with jam), rugelach (cream-cheese dough crescents rolled around jam, nuts, and currants), any kind of gingerbread or molasses cookie, and just about any kind of chocolate cookie in reach. And I'd never refuse a beautiful Parisian macaron. (Among my favorites are Pierre Herme's rose, raspberry, and litchi macarons, known as Ispahan.) But, pushed up against the cookie jar to name my desert-island fave, I'd reach for the chocolate-chippers and hope they'd be 3 inches in diameter, thin, crisp, well-browned, and overloaded with very dark chocolate.