Preheat the oven to 350°. Spray a 13x9 baking pan with cooking spray. Set aside.
Add the flour, salt, and baking soda to a small bowl and whisk.
Add the sugar, brown sugar, and butter to a separate large bowl, and beat with an electric hand mixer until fluffy.
Mix in the eggs individually, then add the vanilla extract and beat until smooth.
Pour in the dry ingredients, and blend at low speed until the batter is just mixed.
Fold in the chopped chocolate candy and M&Ms, then spread the batter evenly into the 13x9 pan.
Bake for 15-20 minutes, until the edges start to turn brown, then cool to room temperature.
Cut out 16 bars, and serve.