Why chill cookie dough before baking? Cold fat melts more slowly in the oven, so cookies often spread less and stay thicker. Resting time also lets the flour soak up more moisture, and many bakers find the flavor gets a bit deeper and more caramel-like after a rest in the fridge. It isn't required for every recipe. But if your cookies keep baking up flat, chilling the dough for a while is usually a good first thing to try.