Preheat the oven to 350°F and line baking sheets with parchment paper.
In a large bowl, cream together the butter, granulated sugar, and brown sugar until smooth. Beat in the egg and vanilla extract.
½ cup unsalted butter, ¼ cup granulated sugar, ⅓ cup light brown sugar, 1 large egg, 1 teaspoon vanilla extract
In a separate bowl, combine the flour, black cocoa powder, corn starch, baking powder, and salt.
1 cup all-purpose flour + 3tbsp, ¼ cup black cocoa powder, ¼ teaspoon baking powder, ¼ teaspoon salt, ½ tablespoon cornstarch
Gradually add the dry ingredients to the wet ingredients and mix until well combined. Fold in the chocolate chips.
⅔ cup semi-sweet chocolate chips
Scoop about 2 tablespoon of dough onto the prepared baking sheets and bake for 8 to 10 minutes in the preheated oven, or until set.
Allow cookies to cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely.