When I was growing up in Kentucky, no-bake cookies were a summer staple—a simple combination of sugar, butter, milk, and cocoa, boiled on the stove and then mixed with peanut butter and rolled oats. Dolloped into bite-size portions, the "dough" sets up all on its own, no oven required. The result is a chewy little oatmeal cookie that's salty/sweet and rich, with a flavor not unlike that of a Reese's cup.
As simple as they sound, problems are all too common. Sometimes no-bake cookies set up as they should, but often they're a sticky mess. Sometimes they turn out crumbly and dry; on other occasions, they're creamy and soft. Most everyone chalks it up to the mystery of baking, or the weather.
Except it's not a mystery, nor is it the weather. When you get down to it, no-bake cookies are simply a type of fudge, which happens to be a wonderfully predictable beast. When fudge's final cooking temperature is too low, its consistency is runny and wet. When its final cooking temperature is too high, its texture is sandy and dry. But right in the middle, when it's cooked just so, fudge can be as soft and chewy as a chocolate cookie.
Unfortunately, a lot of folks are intimidated by the very idea of making fudge, and no-bake cookie recipes go to extreme lengths to avoid revealing the fact that the process is exactly that. So, instead of calling for a thermometer, recipes often try to quantify the process in terms of cooking time. Given the wide range of variables that can influence the timing of a recipe, such vagueness makes success a total crapshoot. That seems completely bonkers to me, when a digital thermometer is dead easy to use and can guarantee consistent results every time. (My favorite is this Polder, because it's good for both stovetop and in-oven projects, whether savory or sweet.)
Aside from setting the cooking temperature to 230°F (110°C), my recipe differs from classic no-bake cookies in a few key ways. First, I omit the butter; the cookies are already ultra rich from peanut butter, so they don't need the added fat. What they need is flavor to round out their fudgy sweetness—which milk can deliver, whether it's skim or whole. Compared with butter, milk is much higher in lactose, a type of sugar that develops a range of tasty toffee notes when boiled above 212°F (100°C).
To bump up the overall flavor, my recipe also calls for dark chocolate in addition to cocoa powder. If you're worried that kids won't like the taste of the dark chocolate, don't be; with all the milk and sugar involved, its flavor will be substantially mellowed in the end. As for the cocoa, it's fine to use natural or Dutch-processed cocoa, but I'm a sucker for the deeper flavor of Dutch. (I like both Cacao Barry Extra Brute and Valrhona.)
Believe it or not, you can make these "cookies" faster than the kind you have to bake—they take only 15 minutes of hands-on time.
Whisk the milk, sugar, cocoa powder, and salt together in a three-quart stainless steel saucier, and cook over medium heat until it's thick, foamy, and exactly 230°F. You don't need to whisk constantly, but you do want to keep the mixture moving to prevent the milk solids from scorching along the bottom.
Add the melted chocolate and peanut butter off the heat, along with a splash of vanilla, and whisk until smooth. Next, stir in the oats with a flexible, heat-resistant spatula.
No-bake cookies are great with either instant or old-fashioned oats, and each can be used to specific effect. With 100% instant oats, the cookies will be thicker and a little less chewy, as the small, precooked oat particles dissolve into the fudge. With 100% rolled oats, the cookies will have a heartier texture that's big on chew. My inner perfectionist loves mixing the two for the best of both worlds, but realistically, the cookies are great either way, and it may take some experimentation to figure out your own preferences.
With a pair of spoons, drop the fudge into cookie-sized portions on a parchment-lined baking sheet. (A cookie scoop makes them look more like clods of dirt.)
Remember, freshly made fudge will be hotter than it looks, so resist the urge to lick the spoon or dig in too soon. Let the cookies cool until they're firm, which can take anywhere from 15 to 25 minutes. The oats will soften as they absorb moisture from the fudge, changing the texture and consistency of the cookies, so don't rush the process.
Once they've firmed up, transfer the cookies to an airtight container. They can be stored at room temperature for a week or two, but will last a little longer in the fridge. While lots of people swear by the taste and texture of no-bake cookies straight from the fridge (akin to my preference for frozen Thin Mints, perhaps), refrigeration is likely a failsafe way to help super-gooey cookies hold their shape when no-thermometer recipes produce inconsistent results.
It's A-OK if you prefer to serve them cold, but with a good recipe and a digital thermometer, you don't have to worry that these chewy, chocolaty, peanut butter–y cookies will turn to mush if they're left out. Although they are inclined to disappear...