In a medium bowl, sift together flour, cocoa powder, baking soda and salt. In a large mixing bowl, using a mixer on medium speed, beat together butter and sugar until creamy - about 1-2 minutes. Beat in vanilla and egg until combined. Reduce mixer speed to low and beat in dry ingredients until combined. Beat in melted chocolate chips until combined.
Divide dough into 24 balls.(I found that it was easier to use a cookie scoop to do this). Place in refrigerator for approximately 30 minutes to allow dough to cool.
Once cooled,flatten a ball in the palm of your hand and place an Oreo in the center; evenly wrap dough around Oreo. Repeat process with remaining dough and Oreos. Place balls on parchment paper lined cookie sheets and bake 10 minutes or until puffy and set. Transfer cookies to wire racks to cool.