Preheat the oven to 350°.

Prepare a 9 x 13 baking pan by spritzing with nonstick cooking spray or oil OR lining with parchment paper.

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

In a mixing bowl, beat the melted butter, sugar, and brown sugar together until well combined. Add the eggs and the vanilla extract, mixing well.

Slowly add the flour mixture to the mixing bowl and beat on low until combined, scraping down the sides as needed.

Fold in the M&Ms, chopped Oreos, and the peanut butter cups.

Press the batter evenly into the prepared baking pan.

Bake for 25 to 30 minutes or until a toothpick inserted in the center comes out clean.

Place the pan on a wire rack and let it cool completely before removing the bars.

To cut the bars, lift the cookies from the baking pan using the parchment paper. For easier slicing, use a serrated plastic knife.