Preheat the oven to 350° F and grease an 8" x 8" pan with cooking spray. Set aside.

With an electric mixer, beat together the butter and the sugars in a large bowl until creamy. Mix in the vanilla, and then add the eggs, one at a time, mixing slowly after each addition.

In a separate bowl, combine the flour, baking soda, and salt. Add this mixture into the butter/sugar mixture slowly, stirring well. Then, fold in the chocolate chips and m&m's, reserving some of each to place on top of the cookie bars once they come out of the oven.

Press about half of the cookie dough into the bottom of the prepared pan. Then, spread the Nutella evenly over the cookie dough. Top with the remaining cookie dough, pressing it to smooth it out over the Nutella.

Bake for 25-30 minutes, until the cookie bars are lightly browned. Top with the remaining chocolate chips and M&m's. Wait about 30 minutes for the bars to cool before cutting and serving. Enjoy!