How to Avoid a Flat Cookie
Take the World's Best Chocolate Chip Cookie for example, from my blog The Better Crumb. This is a recipe that I tweaked dozens of times until I perfected not only the best chocolate chip cookie you've ever had in your life, but the best looking chocolate chip cookie you've ever seen. You know the one... it's puffy and perfectly browned and you know that when you bite into it you will first feel the crunch and then the chewiness on the inside with the chocolate melting warmly in your mouth. As someone once said, "I knew what they were going to taste like before I even took my first bite".
So it's pretty simple and I only stumbled upon this method by accident, but it's one that I now use for every cookie recipe I bake. Yes, of course you need fresh baking soda but you also want to follow the following procedure to discourage overspreading:
After you make your cookie dough, form the dough into balls and freeze them on a parchment lined baking tray for at least two hours or longer. If freezing for longer periods of time, store the cookie dough balls in a Tupperware container in the freezer. Freeze extra parchment lined trays as well.
Fully preheat your oven to ensure it is hot, hot, hot! Pop the frozen, formed cookie dough balls on the parchment lined trays into the hot oven. The heat will start melting the cookie dough, but at a much slower rate because the frozen cookie dough and tray is inhibiting the spreading process "locking" the cookie into its puffy shape.