I adore Boulder bakeshop Tee & Cakes’ cupcakes, but they are not my regular order. I do not think of them at odd hours, I do not (often) order them for breakfast, nor have I spent time pondering their ingredients. This obsession is reserved for another treat in the pastry case: the M&M’s sugar cookie.

I typically find sugar cookies lackluster and anemic-tasting, so it feels odd to have such reverence for Tee & Cake’s version. Co-owner and pastry chef Kim Boos’ cookie is anything but boring: It’s large, full of brightly colored M&M’s (enough to find one in every bite), and has a crackly-crisp exterior with an indulgently soft center. Here’s the kicker: The cookie is tangy with a cream cheese-like flavor that balances the sweetness.

Although I’ve wondered about the cookie’s makeup for years, I finally asked Boos if she would share her secret. She was candid, divulging that cream of tartar, which she uses to stabilize the egg whites, produces the compelling, tangy flavor.

This ingredient (a fine powder derived from tartaric acid found in tart fruits) is a departure for sure. Google sugar cookie recipes and there’s nary a mention of cream of tartar. Only when you do a more refined search do you come up with a handful of options—including this one from Ree Drummond (aka the Pioneer Woman). I’ll work this cookie into my baking repertoire, but it’ll never take the place of Tee & Cakes’ treat.

Extra: Tee & Cakes’ co-owner Brian Wood (who is also Boos’ husband) is a graphic designer who sells his indie-inspired tees, mugs, letterpress prints, and more at the shop.

Got a cookie tip? Tell us where you go when the craving hits.

1932 14th St., Boulder, 720-406-7548

THIS STORY WAS PART OF 5280’s 20 DAYS OF GIVEAWAYS!

Additional comments do not enter you into the giveaway, which ended March 26, 2013.