While flaky sea salt on top is optional, the extra salt on top really brings out the bacon flavor and adds a nice crunch so I highly recommend trying it on at least a few of the cookies the first time you make them. I use Maldon Flaky Sea Salt in any recipe that calls flaky sea salt, such as in my Fudgy Sea Salt Brownies. It's widely available on Amazon or your local grocery store. A small box lasts forever! If you are unable to find flaky sea salt, try coarse sea salt instead.