Preheat your oven to 350°F (175°C) and line a large baking sheet with parchment paper.

In a mixing bowl, combine the melted butter, brown sugar, and granulated sugar, and cream together for about 2-3 minutes until light and fluffy.

Add in the egg and vanilla extract, mixing on low speed until smooth and fully incorporated.

Gently add the all-purpose flour, cocoa powder, baking soda, and salt into the mixing bowl; mix until just combined.

Fold in 2/3 cup of semi-sweet chocolate chips into the dough until evenly distributed.

Drop 8 generous balls of dough onto the prepared baking sheet, leaving space between each. Flatten slightly and sprinkle the remaining chocolate chips on top.

Bake for 10 minutes, keeping an eye on them as they puff slightly but remain soft in the center.

Allow cookies to cool on the baking sheet for about 10 minutes before transferring to a cooling rack.