01 -
Set the oven to 350°F and line a baking sheet with parchment paper.
02 -
Combine butter and chopped dark chocolate in a microwave-safe bowl. Heat in 30-second intervals, stirring each time, until smooth and fully melted. Let cool slightly.
03 -
In a separate bowl, whisk together granulated sugar, brown sugar, egg, and vanilla extract until pale and thoroughly combined to dissolve the sugar fully.
04 -
Pour the melted chocolate mixture into the sugar and egg mixture, stirring until smooth and uniform.
05 -
Sift in flour, cocoa powder, cornstarch, baking powder, and salt. Gently fold until just combined. Fold in chocolate chips or chunks if using.
06 -
Using a cookie scoop or spoon, drop rounded 2-tablespoon portions of dough onto the prepared baking sheet, spacing about 2 inches apart.
07 -
Bake for 8 to 10 minutes, or until edges are set and tops exhibit slight cracking while centers remain soft.
08 -
Allow cookies to rest on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.