Instructions

• Position a rack in the center of the oven and preheat the oven to 350°F. Line two baking sheets with parchment paper.
• In a large bowl, use an electric mixer to cream the room-temperature butter with the packed light brown sugar and granulated sugar until fully combined and smooth, about 3 minutes. Scrape down the bowl as needed.
• Add the egg and egg yolk, then add the ground cinnamon, vanilla extract, baking soda, and salt. Beat until the mixture is completely smooth, about 1 minute, scraping the bowl once if needed.
• Using a wooden spoon or spatula, stir in the all-purpose flour and rolled oats until no streaks of flour remain and the dough is evenly mixed.
• Fold in the chopped dark chocolate until evenly distributed through the dough.
• Using a medium cookie scoop (about 1 1/2 tablespoons), portion the dough onto the prepared baking sheets, placing the scoops at least 2 inches apart.
• Bake the cookies in the preheated oven until the edges are golden brown and the cookies are firm around the edges, 9 to 11 minutes.
• Remove the baking sheet from the oven and let the cookies cool on the baking sheet for about 5 minutes, then transfer the cookies to a wire rack to cool completely before serving.