Preheat oven to 350*F and line an 8 inch square pan with aluminum foil.

To make the crust, crumble the graham crackers into a food processor and process until it's finely ground. Add the flour and brown sugar to the processor and mix. Add the butter until the mixture resembles a fine cornmeal. Add the egg and process until evenly moist. Transfer mixture to prepared pan and push into bottom to form a crust. Bake until firm to the touch, about 20 minutes, then cool on a wire rack in the pan.

To make the topping, in a heavy saucepan over medium-heat, bring the cream to a simmer. Remove from heat and add in the chocolate, stir till smooth and melted. Mix in marshmallows.

Spread mixture evenly over cooled crust and refrigerate for 2 hours, covered by foil. Then take off the foil and cut it into 2 inch by 1.25 inch bars. Remove from pan and put in airtight container for up to 5 days.