Preheat oven to 350.
Line a 9x13 Pan with parchment paper or spray with cooking spray.
Place butter and brown sugar in a medium sized saucepan and heat.
Stir constantly until smooth.
Cool for 5 minutes.
Add Eggs one at a time. Stir until incorporated.
Add Flour, Salt, Baking Soda and Baking powder until combined.
Add half Chocolate Chips.
Add half M&M's and stir.
Transfer mixture to prepared pan.
Add remaining M&M's and remaining chocolate chips.
Bake for 25-30 minutes.
Allow to cool until slightly warm.
Remove from pan and cut into bars