In a medium bowl, whisk together the all-purpose flour, baking soda, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, brown sugar, and granulated sugar until creamy. Add the egg, egg yolk, and vanilla, mixing until well combined and scraping down the sides of the bowl as needed.
With the mixer on low, mix in the flour mixture until just combined. Add the oats and mix on low, scraping the sides as needed. Finally, stir in the chocolate chips on low speed.
Cookies can be baked immediately, but for the best texture, cover and refrigerate the dough for 1 hour (or up to 24 hours). If chilling for more than 2 hours, let the dough sit at room temperature for about 10 minutes before rolling.
When ready to bake, preheat the oven to 350°F and line baking sheets with parchment paper.
Scoop rounded tablespoon-sized portions of dough, roll into balls, and place them on the prepared baking sheets, spacing them 3 inches apart.
Bake for 9-11 minutes, until the centers are just set. Avoid over-baking—slightly under-baking ensures soft cookies. If baking two trays at once, rotate them halfway through.
Let cookies cool on the baking sheet for 5-10 minutes, then transfer to a wire rack to cool completely.