¾cup(105g) all-purpose flour (measure by weight since too little flour will make the cookies spread excessively - see notes in the article above for details)
½teaspoonbaking soda
½teaspoonbaking powder
½teaspoonground cinnamon(optional)
¼teaspoonfine salt
1 cup(100g) rolled oats
⅓cup(35g) quick oats
1cup(142g) dark chocolate, (55-70% cocoa)roughly chopped into chunks, plus extra for topping if desired
Combine butter with brown sugar and vanilla in a large bowl and mix by hand using a wide spatula until smooth and creamy, and a little bit fluffy. The mixture will look more like wet sand than an aerated mixture. Mix in egg until well combined and evenly incorporated.
Combine flour, baking soda, baking powder, cinnamon (if you're using it) and salt in a medium bowl and whisk to blend evenly.
Add the flour mixture to the butter mixture along with the oats and chocolate chips and fold them in until evenly combined.
Place a piece of plastic wrap directly on the surface of the dough in the bowl and refrigerate for 1-2 hours. Do not skip this step or the cookies may spread too much.
Use a 1.35-oz cookie scoop to portion dough and roll into smooth balls for a more polished look and for rounder cookies. Place them onto the prepared baking sheets spacing them 3 inches apart. Do not flatten the dough balls.
Bake for 10-12 minutes until golden around the edges and still slightly gooey in the center (they will set as they cool). Let cookies cool for 3 minutes on the baking sheet and then transfer to a wire rack to cool completely.