Preheat the oven to 350ºF. Line an 8-inch baking pan with parchment paper and spray the paper with nonstick cooking spray.

Melt 1/2 cup of the butter in a small saucepan or in a microwave safe bowl.

Place the graham crackers in a food processor and pulse until they form crumbs. (Alternately, place the crumbs in a ziplock bag and smash the crackers into crumbs with with a rolling pin.) Place the crumbs in a bowl; mix in the 3 tablespoons of sugar and the melted butter. Press the crumbs into the bottom and all the way up the sides of the prepared pan. Bake the crust until it is golden, about 12-15 minutes. Allow the crust to cool completely.

Place the remaining 1/2 cup of butter and the chocolate in a saucepan. Set over medium heat and melt, stirring until smooth. Remove from the heat. Whisk in the remaining 1 cup of sugar, the eggs and the vanilla. Stir in the flour and salt, just until combined. Fold in the pecans.

Pour the brownie batter over the prepared crust. Sprinkle the toffee pieces over the top. Bake for 15 minutes. Sprinkle the coconut on top and bake for an additional 15 minutes, or until a tester in the center of the brownies comes out almost clean. Sprinkle the marshmallows over the top and place back in the oven until the marshmallows are melted.

Remove from the oven and allow the brownies to cool completely before cutting into squares.

Store in an airtight container at room temperature for up to 5 days.