Preheat the oven to 350°F and grease a 13x9-inch pan.

Combine the graham cracker crumbs with the powdered sugar and some of the butter.

Add more butter until you have a sandy texture.

Press the mixture into the bottom of the greased pan.

Bake for 5 minutes or until lightly golden at the edges.

Let the crust cool and set.

Arrange the chocolate bars on top and bake for 3 minutes.

Let it cool for a couple of minutes.

Arrange the marshmallows on top.

Broil for a minute or so, keeping an eye on them the whole time because they can scorch and burn fast.

Let them cool down, then cut and serve.