Step 1

Begin by preheating your oven to 350 degrees F. Line a 9×13 inch baking pan with parchment paper. Fold the parchment paper so that it fits snugly in the pan. I use two sheets – one folded to fit the length of the pan and another folded to fit across the pan. Allow the excess parchment paper to hang out over the side of the pan. Coat the parchment paper with a thin layer of non-stick cooking spray. Once the confection is firm, use the excess parchment to lift the whole block out of the pan to make it easy to cut into squares.

Step 2

In a large mixing bowl, beat together the butter, peanut butter, sugar and brown sugar until light and fluffy.

Step 3

Add the vanilla, a whole large egg, and one large egg yolk to the butter mixture. Beat to combine.

Step 4

Finally, add the flour, baking soda, and quick oats. If you used unsalted butter at the beginning of the recipe, add 1/4 teaspoon of salt here too. Beat the dry ingredients into the wet ingredients until well mixed.

Step 5

Measure the mini white chocolate chips, 3/4 cup of the M&Ms, and half of the sprinkles into the cookie dough. Stir well to combine.

Step 6

Transfer the cookie dough to the prepared baking pan and press it into the pan, being sure to get into the corners.

Step 7

Top the dough with the remaining M&Ms and sprinkles.

Step 8

Bake for 15 minutes or until the squares are lightly browned on the edges. Remove the pan from the oven and allow it to cool for at least 30 minutes before attempting to slice it into squares.