Preheat the oven to 325°F. In a large bowl using a mixer, cream together the butter and sugars for 1 minute. Add the eggs and vanilla and mix until combined. Add the flour, baking soda and stir mixture just until combined. Fold in the chocolate chips and M&M’s (saving about 1/4 cup for the top). For thick bars, line a 9×13″ pan with parchment paper or foil or spray. For thinner bars, line a 15×10″ pan. Scoop cookie dough into the pan and press down evenly. Then place extra M&M’s and chocolate chips on the top. Bake for 30-35 minutes for a 9×13″ pan or 20 minutes for a 15×10″ pan, or until the top is barely golden brown. Allow to cool completely, then remove and slice.