Preheat the oven to 325°F. Line baking sheets with parchment paper or silpat mats.
In a large bowl, use an electric mixer to combine the butter and sugars. Add the egg, egg yolk and vanilla, beating until well combined.
In a separate bowl, whisk together the flour, oats, baking powder, baking soda and salt. Add to the wet mixture and beat until everything is well incorporated, scraping down the sides of the bowl as needed. Stir in the chocolate chips.
Form the dough into heaping teaspoon sized balls and place them about 2 inches apart on the prepared baking sheets. Using your palm, gently press down.
Bake for 12 to 15 minutes, or until the cookies begin to brown at the edges. Cool on the cookie sheet for 10 minutes, then transfer to a wire rack to cool completely.