What size cookie cutter should I use?

You can use whatever size you want! I used a 3 inch cookie cutter to make a pretty large cookie but it depends on how big a cookie you want.

I used 2.5 inch cutter, but a 3 inch cutter is probably what they used in the recipe because I ended up with about 16 cookies instead of the 12 made with this recipe. I like a smaller cookie.