Preheat your oven to 350°F (175°C).

Grease a 9×13 baking pan with non-stick spray or butter.

Combine graham cracker crumbs, powdered sugar, and 8 tablespoons of melted butter in a bowl. Mix until evenly moistened.

Press firmly along the bottom (and optionally up the sides) of the pan to form a compact crust.

Bake for 5–8 minutes, until the edges start to turn light golden. The crust will firm up upon cooling.

Let the crust cool for a few minutes.

Arrange four Hershey’s bars to cover the crust fully.

Bake for about 3 minutes, until the chocolate just begins to melt and shine.

Remove from the oven; space mini marshmallows closely across the melted chocolate.

Switch the oven to broil.

Return the pan to the oven for 1.5–2 minutes, watching closely until marshmallows are puffed and golden. Remove immediately.

Allow the bars to cool completely—chill in the fridge to speed it up and help cleanup.

Use a warm, wet knife for cleaner cuts: heat under hot water, dry, and slice. Wipe between cuts if needed.