There's a lot of things that can throw off baking recipes --
- Regional variations in flour hardness. 'All purpose' flour from the US South tends to be softer than brands from other areas.
- The humidity and temperature.
- Altitude (affects the boiling point of water, which will require adjusting baking times and possibly leavening agents)
- How you measure your flour -- I'm lazy and use scoop & sweep -- my mom, however, would use spoon and sweep.
- Size of your eggs. Most recipes in the US assume 'Large' eggs unless otherwise specified.
- Type of salt used. Most recipes in the US assume table salt unless otherwise specified.
- How you mix the dough, and how long you mix it.
- How long you rest the dough before rolling out.
In your case, for rolled doughs:
- temperature of the dough. (you want it chilled, but not so cold that it crumbles)
- work surface / rolling pin material (specific to your problem, will affect how much things stick, and how they retain/transfer heat)
You might also want to see Baking 911 : Cookies Problems and Baking 911 : Rolled Cookies
There are a few things I can think of. The first is, are you sure your oven is at the right temperature? Although your oven may beep that it's preheated, without checking it with an oven or infrared thermometer you can't be sure that it's actually at the temperature you need - and even if it is at that temperature where the sensor is, it might not be the same temperature elsewhere in the oven. Try moving the rack you're using one or two levels closer to or further from the element and see if it makes a difference (further will probably be better if you're trying to increase spread). My oven has a 50-75°F range from the top rack to the bottom - a major difference when it comes to baking! Understanding my oven's temperature range changed my baking outcomes significantly.
Second, are you letting the dough come to room temperature before baking? I've found that the colder my dough, the less spread I get.
On Betty Crocker's site, there is an FAQ and under "Why don't my cookies spread", they recommend using an aluminum sheet - the darker the cookie sheet, apparently, the less spread you will get. I haven't tested this personally, but I trust the source :) I get good spread on my silpat baking sheets, for what it's worth.
The only other thing I can think of is your butter, is it truly softened, or is it a hard block, or is it melted? I'm not an experienced enough baker to explain the science behind the differences as they relate to baking, but I do know that those three options will produce significantly different results. I believe that if your butter is too cold, they won't spread as much as they could - but hopefully someone can chime in and confirm or deny that.
Oh, and I asked a friend of mine who's a baker - she said that it's possible that your baking soda is old, and that could cause it, but I don't know from first hand experience if that's possible or not. I trust her judgment though, as she's my go-to with baking questions and she's never led me astray.
Best Answer
I had the same problem until I learned how to stop it. Here is how. When you drop your dollop of cookie dough onto your cookie sheet, press it down so it's "pre-spread" out. Then you'll more reliably have right sized and shaped cookies because the dollop isn't melting down so much. You don't need to squash it all out full sized, just push it down so it's not ball shaped anymore.
It helped me a lot with choco-chip cookies.