Preheat the oven to 325 degrees.

Prepare a 9x 13 pan by lining with parchment paper. Create a sling to easily lift bars out when baked.

In a medium size bowl, mix together the flour, baking soda, powder and salt. Set aside.

In a large bowl or stand up mixing bowl, add the melted butter, brown sugar and granulated sugar. Mix until incorporated.

Add the eggs, egg yolk, and vanilla to the butter mixture. Mix in.

Add the flour mixture into the butter mixture, one cup at a time.

Add the chocolate chunks and ½ cup of the M & M candies. (Reserve the remaining for the top.)

Press the cookie dough evenly into the bottom of the prepared pan. Sprinkle the top of the dough with the chocolate chips and remaining M & M’s. Gently press into dough.

Bake at 325 for about 25-30 minutes or until lightly golden brown. Remove from the oven and place on a wire rack to completely cool before removing from the pan.

Remove the bars from the pan using the sling.

Place the bars on a cutting board and cut cooled bars into 16 pieces. Sprinkle the bars with flaky sea salt.