Coat a 9x13-inch baking dish with cooking spray. Set aside.

Place cereal in a large bowl. Add the chocolate chips. Remove 3 cups of mini marshmallows from the bag. Toss 2 1/2 cups of the marshmallows with the cereal and chocolate chips. Set aside the other 1/2 cup to press into the top of the bars later on.

In a large pot, melt the butter over medium-low heat. Add the remaining marshmallows. Stir constantly until just barely melted. Remove from heat. Let rest 2 minutes to cool slightly.

Pour the melted marshmallows over the cereal mixture. Stir until evenly coated. Pour into the prepared pan and flatten with a greased spatula or rolling pin.

Separate Hershey's squares and then cut them in half. Press the chocolate squares and reserved 1/2 cup of mini marshmallows into the top of the krispie treats. TIP: Place a layer of wax paper on top (to minimize the sticky mess) and then press or roll with rolling pin.

Cool completely, then cut into squares and serve. Cover and store any leftovers at room temperature up to 5 days.