Step 1

Preheat the oven to 350°F. Prepare an 8-inch square pan or a 9-inch square pan with two sheets of parchment paper, leaving an overhang on each side for easy lifting.

Step 2

In a medium mixing bowl, add graham cracker crumbs and melted butter. Mix well with a fork until well combined.

Step 3

Transfer the mixture into the prepared pan. Use a flat bottomed measuring cup and press into the pan to create a packed, even layer.

Step 4

Place into the oven to bake for 14 minutes. Remove from the oven and allow to cool to just barely warm.

Step 5

In a medium mixing bowl, add the chopped chocolate and heavy cream.

Step 6

Place the bowl into the microwave and microwave in 30 second intervals, stirring in between, until fully melted and smooth.

Step 7

Immediately pour the chocolate over the slightly cooled down graham cracker base.

Step 8

Place into the fridge for 1-2 hours to set.

Step 9

Preheat the oven to 400°F.

Step 10

When the chocolate ganache is mostly set (slightly soft is okay), remove from the fridge and add the marshmallows on top.

Step 11

If using, add the milk chocolate pieces, graham cracker pieces, and milk chocolate chips on top.

Step 12

Place into the preheated oven to bake for 10 minutes, until marshmallows are toasty. Remove from the oven and allow the bars to fully cool to room temperature (about 1 hour) before slicing with a warm knife.