Make a test cookie. I can’t tell you how many times I filled an entire mold with cookies only to find after baking that I should have done something different – space them out more or less, cool the dough more, adjust the time Cooking. (I often catch myself shouting this on my TV while watching “The Great British Baking Show.”) Especially if you’re working with an unfamiliar recipe, do yourself a favor and sacrifice a cookie or two as the guinea pigs to see how they cook. . The time commitment is not long, as the cookies bake quite quickly, and you might end up saving yourself some heartache in the long run. If you have a smaller mold, like a quarter sheet or a jam mold, use it for the test batch, while you prepare the rest of the dough on your half-sheets.