Preheat your oven to 350 degrees Fahrenheit and grease a 9×13 baking pan with non-stick butter spray.

In a medium mixing bowl, combine graham cracker crumbs and powdered sugar. Gradually mix in melted butter until the texture is moist yet crumbly.

Press the mixture firmly into the bottom and up the sides of the greased baking pan.

Bake the crust for 5 to 8 minutes until edges are slightly golden.

Arrange chocolate bars evenly over the cooled crust and bake for about 3 minutes until melted.

Spread mini marshmallows over the melted chocolate and broil for about 2 minutes until golden brown.

Allow the S'mores Bars to cool completely at room temperature.

For cleaner cuts, refrigerate the cooled bars for a short while.

Using a warm knife, cut the S'mores Bars into squares for serving.