Make the dough:

1. Using a mixer, cream together the butter and sugar. It should be well combined and creamy.
2. Beat in the egg and vanilla and mix. It should look creamy once combined.
3. In a separate mixing bowl whisk together the dry ingredients – flour, cocoa, baking soda and cornstarch.
4. Add the dry ingredients to the wet and mix.
5. Gently mix in the white and semi-sweet chocolate chips.
6. Cover and chill in the fridge for at least 3 hours before baking.

To Bake the cookies:

1. Pre-heat the oven to 350°F.
2. Line a baking sheet with parchment paper and set aside
3. Using your hands form the dough into 1 inch balls. Work quickly to avoid warming up the dough too much – you want to make sure the dough is still relatively cold when you put them into the oven. Don’t over touch the dough (if mistakes happen and the dough gets sticky or too warm, just throw them back in the fridge for a bit before baking).
4. Place dough balls evenly on a parchment lined baking sheet, making sure to leave plenty of space between each (like 1-2″ space). You need to leave enough room for your cookies to expand. (You may have to bake the cookies in little batches and that’s ok! Got to leave room!)
5. Place into the oven to bake for 9-10 minutes.
6. Remove baking sheet from the oven and allow to cool for a couple minutes.
7. After about 10 minutes, place the cookies on a wire rack to continue to cool.