Preheat oven to 325 degrees. Line a baking sheet with parchment or a silicone baking mat.
In a large mixing bowl, beat together butter and sugars. Add egg, egg yolk and vanilla. Continue to beat until well combined.
Add flour, oatmeal, baking powder, baking soda and salt. Mix until just combined. Stir in chocolate chips.
Scoop dough into 2 Tablespoon sized balls. Shape balls, making them more tall than flat. Place in freezer for 15 minutes. Remove from freezer and place on baking sheet.
Bake for 13-16 minutes until edges are golden and centers are set. Cool on baking sheet for 5 minutes before removing to a cooling rack.
Recipe by Crumbs and Chaos at http://www.crumbsandchaos.dreamhosters.com/2015/03/triple-chip-oatmeal-cookies/