Preheat oven to 325°F and grease a 9x13 pan. Lightly dust with flour or line with foil.
Cream butter and sugar in a large bowl. Add in eggs and vanilla and stir until combined. In a separate bowl, whisk together the flour, baking powder and salt. Pour into the butter mixture and stir. Fold in chocolate chips and M&M’s.
Press 1/2 the dough into the pan with flour on your hands. Cut the Reese's into small pieces and lay them on top of the dough. Place the remaining cookie dough on top of the Reese's. You can add extra M&M’s on top if you’d like.
Bake for 30-40 minutes or until lightly browned. Oven temps will vary. Test with a tooth pick. The dough should be soft in the center.
Allow bars to cool and then enjoy with a cold glass of milk!
Alternatively you could use reeses pieces instead of peanut butter m&m's.