About ¼ inch of chocolate works just fine. Use a spoon to spread the chocolate a little up the sides of the liner. We then put the tins into the fridge to allow the chocolate to solidify.
While the chocolate liners are solidifying in the fridge, mix together the peanut butter, graham cracker crumbs, powdered sugar and pinch of salt in a bowl.
Marshmallow fluff naturally flattens out and runs at room temperature so let these sit for 5-10 minutes so the marshmallow flattens out a bit on top of the peanut butter.