Mix dry ingredients in a bowl.
Mix butter, sugar, and brown sugar in another, larger bowl and blend them until they're creamed. I use a hand-mixer, my trusty SunBeam that's lasted over two decades now. I also have a firm plastic spatula that I use to occasionally press it all back together.
Blend in the egg. If increasing the batch size, blend in one egg at a time.
Blend in the vanilla and mint oil.
Fold the dry ingredients into the wet bowl, about a third at a time, and blend them together, I use the mixer for this as well.
Roll dough into balls, and either bake them or freeze them for baking later.
Preheat the oven to 350°F. Place them onto an ungreased cookie sheet, leaving room for them to expand. Bake them until they're done, about 12 minutes.
Using a spatula, put them onto plates to cool.
I've taken to making half batches of cookies, or perhaps you could call them one egg cookies. Much more reasonable amount. Can then be scaled up easily if desired.
I'm no longer able to find Guittard mint chips, so I decided to use mint extract instead. This recipe is just for the dough, I plan to use it for Mint Chocolate Chip cookies as well. I had several open bottles of mint extract and mint oil, I decided to start with Humco Pepperment Oil, which is pure peppermint oil.