Step 1

Preheat oven to 350F. Line an 8-by-8-inch baking pan with aluminum foil, spray with cooking spray; set aside.

Step 2

In a large, microwave-safe bowl melt the butter, about 1 minute on high power.

Step 3

Wait momentarily before adding the egg so you don’t scramble it. Add the egg, brown sugar, vanilla, and whisk until smooth.

Step 4

Add the flour and stir until just combined, don’t overmix.

Step 5

Stir in the Oreos.

Step 6

Turn batter out into prepared pan, smoothing the top lightly with a spatula.

Step 7

Evenly sprinkle the M&M's over the top, lightly pressing them down with your finger or a spatula.

Step 8

Bake for about 20 to 22 minutes, or until done based on add-ins used. Top should be set and edges slightly firm. A toothpick inserted in the center (if you can find a bare patch to test) should come out clean, or with a few moist crumbs, but no batter.

Step 9

Allow bars to cool in pan for at least 30 minutes before slicing and serving.