Preheat your oven to 325 degrees F.
Line an 8-inch-square baking pan with foil so that it hangs over the edges and spray it with nonstick cooking spray.
Use a medium-sized bowl to mix together the melted butter, graham cracker crumbs and sugar.
Press the crumb mixture evenly on the bottom of the pan.
Bake until golden, or for about 20 minutes. Remove and set aside.
Raise the oven temperature to 350 degrees F.
Meanwhile, use a medium-sized bowl and mix the brownie mixture together, then gently fold in the raspberries.
Pour the batter over the graham cracker crust.
Bake the brownie mixture for about 25 minutes (based on your brownie mix), or until a toothpick inserted in the middle of the brownie comes out clean.
Remove the brownie and place the oven on broil.
Meanwhile, break the two graham crackers into small pieces and arrange them in a single layer on top of the brownie.
Next arrange the mini marshmallows evenly over the top of the graham crackers.
Place the pan back in the oven, just for a few minutes, until the marshmallows begin to brown. Keep a close watch on them so they don’t burn under the broiler.
Remove from the oven and cool completely.
Remove from the pan using the overhanging foil and cut into bars to serve.