Melt butter. Set aside to cool for a minute or two.
Prepare a 9×13 baking dish with non-stick spray. Set aside.
In a small bowl, whisk together flour, salt and baking soda. Set aside.
Using either a stand mixer or a hand mixer, mix together the melted butter, brown sugar and white sugar. Add egg and extract. Mix until smooth. Continue to mix, adding the flour mixture in small amounts, until all combined.
Stir in the chocolate chips and ½ C m&ms.
Press the mixture into prepared baking pan evenly.
Lightly press the remaining mms onto the surface of the dough. (this will ensure you see the bright colors on top of the bars).
Bake 25-30 minutes until lightly browned and sides begin to pull away from the sides of the pan.