In a large mixing bowl, beat together 1 cup of room temperature unsalted butter, 1/2 cup granulated sugar, and 1 cup brown sugar until creamy and fluffy, about 2-3 minutes. Add in 1 large egg and 2 teaspoons of vanilla extract, mixing until just combined.

In a separate bowl, whisk together 1 1/4 cups all-purpose flour, 1/2 cup natural cocoa powder, 1/2 teaspoon baking soda, and 1/4 teaspoon salt. Gradually blend the dry ingredients into the wet mixture, followed by 2-3 tablespoons of milk and 1 cup of semi-sweet chocolate chips, mixing until well incorporated.

Once your dough is mixed, cover the bowl with plastic wrap or a clean kitchen towel and refrigerate it for at least 3 hours or overnight.

When ready to bake, preheat your oven to 350°F (175°C).

After the chilling period, use a cookie scoop or a tablespoon to portion out the dough, forming each piece into taller balls for thicker cookies. Place the dough balls about 2 inches apart on a lined or greased baking sheet.

Slide the baking sheet into your preheated oven and bake the cookies for 11-12 minutes, or until the edges are set and the centers appear slightly soft.

Allow the cookies to cool on the tray for a few minutes before transferring them to a wire rack to cool completely.