Preheat the oven to 350°.
Beat butter and brown sugar.
Add egg and vanilla and mix well.
Add flour, baking powder and salt.
Mix until you cannot see the flour.
Crush the graham crackers.
Add the graham crackers and mix by hand.
Divide the dough in half. Add a little from one half to the other. The smaller dough is the top and the heavier dough is the bottom.
Place the smaller dough into an 8x8 pan. Using parchment paper push the dough to the edges.
Turn the pan upside down and drop the dough out on the parchment. Set aside.
Put the other half of the dough into the bottom of the pan and using another piece of parchment paper push the dough to the edges of the pan.
Layer on the chocolate bars.
Cut the large marshmallows into fourths and layer onto the chocolate bars.
Carefully take the other dough and turn it upside down on top of the marshmallows.
Bake for 30 minutes until golden brown.
Cool and then cut and serve.