Preheat your oven to 350°F (175°C).
In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.
In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the semi-sweet and white chocolate chips until evenly distributed.
Drop rounded tablespoons of dough onto ungreased baking sheets, spacing them about 2 inches apart.
Bake for 10-12 minutes, or until the edges are set but the centers are still soft.
Remove from the oven and let the cookies cool on the baking sheets for 5 minutes before transferring them to wire racks to cool completely.