1. Mix the dry ingredients in a medium bowl, set aside.
2. In the bowl of a stand mixer fitted with a paddle, add the cooled butter and the white and brown sugars. Beat the butter and sugars on medium speed for 1 minute until creamy.
3. Add the whole egg, egg yolk, milk and vanilla extract and mix untill well combined.
4. Add half of the flour mixture and blend on low speed until combined. Add the other half of the flour and mix until fully blended.
5. Mix on medium speed for 10 seconds to fully blend the batter.
6. Add the chocolate chips and mix on low until incorporated.
7. Chill the dough in the refrigerator until firm, approximately 1 hour.
8. Preheat oven to 180°C fan. Prepare 2-3 baking sheets by lining parchment paper or silicon baking mats.
9. Scoop out rounded tablespoons of dough and place on the sheets, arranging about 9 cookies per sheet.
10. Bake for 8-10 minutes, rotating the pans after 8 minutes. Make sure cookies are browned and slightly firm on the edges.
11. Remove from the oven and cool the cookies on the pans for atleast 3 minutes. Carefully, move the cookies to a wire rack and cool completely.
12. Store cooked cookies in an airtight container or in the freezer in a freezer safe bag.

Note: Do not leave in humid kitchen for too long. Sugar is hygroscopic and will begin to absorb moisture from the air and the cookies will become soggy and crumbly. Carefully place in a tupperware with parchment between layers of cookies and store in the fridge.