Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
In a large mixing bowl, combine the cake mix, eggs, and vegetable oil until a thick dough forms.
Add blue food coloring a little at a time until the desired Cookie Monster blue color is achieved.
Fold in the chocolate chips and crushed sandwich cookies if using.
Scoop tablespoon-sized portions of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake for 9 to 11 minutes, or until the edges are set and the centers still look slightly soft.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.
If desired, decorate with candy eyes and additional chocolate chips while the cookies are still slightly warm.
Cool completely before serving or storing.