3/4–1 cup chopped dark or milk chocolate bar (chocolate chips will work fine but I think bars work much better)
In the bowl of a stand mixer or using a hand mixer, cream together the butter, sugar, and brown sugar until light and fluffy, about two minutes. Scrape down the bowl and beat in the egg followed by the vanilla.
In a separate bowl, whisk together the flour, oats, salt, baking soda, and whatever mix-ins you’re using. Add the dry ingredients into the wet and mix just until combined, scraping down the bowl a few times throughout mixing.
Place the cookie dough into the fridge to chill for about one hour.
Preheat oven to 375ºF and line two large baking sheets with parchment paper.
Using a 60 milliliter scoop, scoop six cookies onto each baking sheet making sure to leave space between each. Press the tops of the cookies down a little with the palm of your hand or the back of a fork just to flatten a bit then bake the cookies for 12 to 14 minutes or until golden around the edges and still soft in the middle, turning and swapping the pans halfway through.
Cool the cookies for five minutes on the baking sheets then remove to a cooling rack to cool completely.
Continue scooping and baking the cookies until all the dough is used up.