Preheat oven to 375 degrees.
In a large bowl cream together butter, brown sugar and granulated sugar for 2 minutes on medium speed.
Add in eggs and vanilla and mix until well blended.
Mix in flour, baking soda and salt until almost incorporated.
Add in mini chocolate chips and 1/2 cup M&M's and finish mixing until the flour is just incorporated.
Lightly spray a half size baking sheet.
Spread cookie dough onto baking sheet pressing it into an even layer.
Press the remaining M&M's into the top of dough spreading them throughout.
Bake for 18-20 minutes or until lightly golden brown.
Let them cool for 20 minutes on the baking sheet before cutting into 12 squares.
*This recipe can be doubled and baked in a full size baking sheet.