Brown the Butter: Measure out the butter and brown it in a small saucepan over medium heat until it turns a deep golden colour and smells nutty.
Mix with Sugar: In a medium-sized mixing bowl, add the sugar. Pour the browned butter over the sugar and mix until combined.
Cool and Add Egg Yolks: Allow the mixture to cool slightly, then add the egg and egg yolk and mix until smooth.
Incorporate Vanilla: Stir in the vanilla extract.
Add Dry Ingredients: Gradually add the whole wheat flour, white flour, baking soda, salt and rolled oats to the wet mixture, mixing until just incorporated.
Fold in Chocolate Chunks: Gently fold in the chocolate chunks, being careful not to over-mix.
Rest the Dough: Let the cookie dough chill for 2+ hours to hydrate the whole grain flour and develop flavour.
Preheat the Oven: Once ready to bake, preheat your oven to 350°F (175°C).
Shape the Cookies: Scoop the dough into balls, about the size of a heaping tablespoon or 50 grams each, and place them on a baking sheet. Press down slightly. Optionally, top with a sprinkle of flaky salt.
Bake: Bake at 350°F for 10-15 minutes, depending on your oven and dough ball size. The cookies should be slightly golden on the outside and puffed in the middle.
Cool: After baking, remove the cookies from the oven and let them cool on the baking sheet for about 5 minutes before transferring them to a cooling rack.