Cream together the butter, granulated sugar and brown sugar.
Add the egg and vanilla. Mix until light in color and creamy.
Add in the dry ingredients (flour, cocoa, baking soda and salt), mix into the dough. Mix until completely combined. The dough will be soft.
Fold in the whtie chocolate chips.
Scoop or roll the cookie dough out into equal sized balls. Arrange on a cookie sheet. Add extra white chocolate chips and the crushed peppermints to the top of the cookie dough.
Bake at 350° for 7-9 minutes or until the cookies are puffy and no longer glossy on top. Allow the cookies to cool on the pan for at least 15 mintues before serving.