Preheat the oven to 350°F (175°C). Spray a 9-inch square baking dish with cooking spray.

In a small bowl, stir together 8 tablespoons salted butter (melted) and 1/2 teaspoon vanilla extract.

Pour the butter-vanilla mixture into the prepared baking dish.

Evenly scatter 1 2/3 cups graham cracker crumbs over the butter mixture, then use a rubber spatula (or the bottom of a measuring cup) to press the crumbs firmly and evenly into the butter to form a crust.

Sprinkle 1 1/4 cups sweetened shredded coconut evenly over the graham-cracker crust.

In a separate bowl, combine 1 1/2 cups semi-sweet chocolate chips and 1 1/4 cups salted peanuts, then sprinkle that mixture evenly over the coconut layer.

Evenly drizzle the contents of 1 (14 ounce) can sweetened condensed milk over the chocolate chips and peanuts so the top is covered as uniformly as possible.

Bake in the preheated oven for 30 minutes.

Remove from the oven and let the bars cool completely in the pan before slicing and serving.