In a large mixing bowl, cream together salted butter, light brown sugar, and granulated sugar until light and fluffy.

Add egg and vanilla extract; whisk until fully combined.

In a separate bowl, whisk together all-purpose flour, cocoa powder, baking soda, and salt.

Gradually add dry ingredients to the wet mixture, mixing until just incorporated.

Fold in mini dark chocolate chips and dark chocolate chips.

Wrap the dough in cling wrap and refrigerate for 2-3 hours.

Preheat oven to 155-180°C (315-350°F). Scoop chilled dough onto baking sheets, spaced apart.

Bake for 10-12 minutes, until edges are slightly browned; let cool before transferring to a wire rack.