Preheat the oven to 350°F / 175ºC and grease a 9 x 9 inch baking tin.

Make a layer of Graham crackers on the base of the tin. You want only a single layer.

Follow the instruction on the box of brownie mix to make the batter then fold in the chopped Hershey bars.

Pour the brownie mixture over the Graham crackers and spread into a even layer.

Bake in the oven for around 30 minutes until a toothpick inserted into the center comes out clean.

Remove from the oven and lay pieces of the Herseys chocolate on top of the hot brownie.

Turn on the broiler.

Place marshmallows in an even layer on top of the cooked brownie then place under the broiler just for a minute or two until the marshmallows are toasted and soft.

Allow to cool slightly before slicing and serving.