Preheat the oven to 350 degrees

Line a 9x13 baking pan with parchment paper, with the parchment paper extending about two inches over the sides of the pan, for easy removal of the bars after baking. Set the pan aside to prepare the crust.

In a microwave-safe bowl, melt the butter. (About 30-45 seconds) Pour the melted butter into a medium bowl, and stir in the crushed graham cracker crumbs to combine. Stir until the crumbs look like wet sand.

Evenly pour the crust over the parchment paper and press into the pan with a spatula. Evenly pour the chocolate chips over the graham cracker crust, then repeat with the other two flavors of chips. Sprinkle the coconut flakes over the chips, evenly distributing the coconut. Sprinkle nuts over the top of layers if you are using them.

Once you have layers in the baking pan, pour the condensed milk over the top of the mixture, spreading with a rubber spatula as you pour.

Place in the center of the heated oven, on the middle rack, and bake for 25-28 minutes, until the bars turn light golden brown in color. Remove the pan from the oven, and allow the bars to cool before cutting.