Why didn't my cookies crack on the top like the ones in this recipe when I made it?

First of all, let me state that its most likely not something you're misinterpreting...the recipe isn't very specific. Something I've learned about baking is that even the smallest nuance can make such a difference. And sometimes....its impossible to tell what's going wrong without actually making it. First of all, what kind of chocolate are you using? Good quality dark chocolate bar or cheap semisweet chocolate chips? They're very different products and could be making a difference. Are you using a stand mixer, a hand mixer or your hand when beating the sugar and eggs? There really shouldn't be a time limit but a visual cue in this step. You're looking for something that resembles soft whipped cream and should fall in thick ribbons on itself. It should be nearly tripled in volume. I'm assuming this is what they're looking for, since they don't explicitly state it. IF the recipe is looking for maximum volume in the meringue, its important that you maintain the volume. Are you pouring in the melted chocolate while its still hot or is it completely cook? I would recommend cooling the mixture slightly, but making sure its still warm when pouring it in. Are you mixing the dry ingredients in with the mixer? And if so, for how long? My brownie recipe uses a similar procedure and I don't use the mixer to incorporate the dry ingredients, I sift them over the batter and fold it in by hand. I then only mix it until just incorporated.

I would give those a try and see what happens. Share your results, because it helps all of us!

My first question, one that I usually ask whenever things come out soft and spongy: did you check the oven temp to make sure it's accurate? It sounds like it might not be hot enough.

Second question: how are you measuring out the ingredients? Weighing out ingredients usually ensures better more consistent results. And no 2 people scoop the same way :)

Did you beat the eggs and sugar for 15 minutes as the recipe says? I read somewhere that it's actually a meringue, achieved by a thorough beating of the eggs, that causes brownie tops to crackle on the top. The long beating time suggested in the recipe may be the answer. ;o)