Preheat oven to 350°F. Grease an 8x8'' baking pan (or line with parchment paper).

Add flour, cocoa powder, baking soda and salt to a small bowl and stir to combine.

To a large mixing bowl add butter, brown sugar and granulated sugar. Beat with electric mixers (or in your stand mixer) until well creamed together, about 3 minutes. Add egg and vanilla and mix well.

Add dry ingredients and mix just until incorporated. Stir in Oreos and white chocolate chips. Press dough into pan.

Bake for about 18-25 minutes or until a toothpick inserted in the center comes out clean.