2. Silicone baking sheets. No more greasing your cookie sheet or lining it with parchment paper, silicone baking sheets are a one-time investment that you will absolutely love, and a great way to go "green." These non-stick sheets help conduct the heat evenly, can handle every type of oven, and are also ideal for candies. I recommend having two in the same size as your cookie sheets.
3. Cooling rack. Remember, just because you've pulled something out of the oven doesn't mean it isn't still baking! Removing your cookies from the baking sheet and transferring them to a cooling rack is one of the most important steps in baking. Unfortunately, it's one of the most neglected. Cooling racks are extremely inexpensive and, again, a one-time investment.
Baking is a wonderful hobby, one that brings joy to the baker and everyone around her too. And the more you stick with it, the more you will master the art and science of your own creations. If you're investing your time in the kitchen to create something wonderful, invest a little in the equipment you use. I promise, you won't regret it.
Fine print: The links I've provided are just examples. I am not endorsing or recommending any particular brand.
