Preheat oven to 325 degrees Fahrenheit.

In a large bowl, cream together softened butter and both granulated and brown sugars until light and fluffy.

Beat in eggs one at a time, then stir in vanilla extract.

In a separate bowl, sift together flour, cocoa powder, baking soda, baking powder, and salt.

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

Stir in white chocolate chips.

Drop by tablespoonfuls onto ungreased baking sheets.

Bake for 10-15 minutes, or until edges are lightly golden.

Let cookies cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.

Store in an airtight container.