Combine the rolled oats, whole wheat flour, whey protein, baking soda, and cocoa powder in a mixing bowl.
Add the salted butter, brown sugar, and castor sugar to another bowl and mix until well combined.
Add the egg and vanilla extract, then mix until smooth.
Add milk gradually and mix until combined.
Add the wet mixture to the dry ingredients.
Mix until a soft cookie dough forms.
Cover the cookie dough and refrigerate for 30 minutes.
Line a baking tray with parchment paper and Preheat the oven to 350°F (180°C).
Shape the dough into evenly sized rounds and arrange them on the prepared baking tray with space between each cookie.
Gently press each cookie with your fingers and top with chocolate chips.
Bake at 350°F (180°C) for 20 minutes.
Allow the cookies to rest on the baking tray for 3–4 minutes after baking.
Transfer the cookies from the baking tray to a cooling rack.
Serve and enjoy.
