Here are our tips to determining when cookies and brownies are done.
We think most cookies are best when they are chewy. This means taking them out of the oven when they are slightly underdone—in fact, the cookies are often so soft they will droop over the end of a spatula. Bake cookies on parchment and cool on baking sheet for a few minutes; after they have set up slightly, slide the parchment onto a cooling rack. if the cookies have crevices, the crevices should appear moist. When baking smooth cookies, look at the edges, which should be lightly browned; the center should be set but not fully dry.
Overbaked brownies are dry and chalky and the chocolate flavor is diminished. Use the skewer test to determine doneness, but look for moist sticky crumbs.