Preheat oven to 325 degrees. Line a cookie sheet with parchment paper.
Beat together butter, sugar and brown sugar until creamy.
Add egg and vanilla extract. Beat until well blended.
Add flour, baking soda and salt. Beat until dough begins to form a ball.
Remove ball from mixing bowl and split into 3 equal parts.
Leave one of the portions of dough plain.
Add black cocoa powder to one of the dough portions.
Add the crushed oreo to the last portion of dough. Stir only until mixed in. You want to still be able to see some of the dough so it has a speckled appearance.
Roll ½ teaspoon size dough balls with each type of dough.
Take one dough ball from each of the three types of dough and roll them together.
Bake in preheated oven for 8-10 minutes or until edges start to become golden.
Remove cookies to a cooling rack.
