Preheat your oven to 350°F (175°C) and prepare a 9x13 inch baking dish by greasing it lightly or lining it with parchment paper.
In a medium mixing bowl, combine the graham cracker crumbs, shredded coconut, melted butter, and brown sugar. Stir until the mixture resembles wet sand.
Press the crust mixture firmly and evenly into the bottom of the prepared baking dish.
In another bowl, whisk together the sweetened condensed milk, vanilla extract, and a pinch of sea salt until smooth.
Carefully pour the sweetened condensed milk mixture over the graham cracker crust, spreading it evenly.
Sprinkle the semisweet chocolate chips and butterscotch chips over the condensed milk layer. If using nuts, scatter them on top.
Bake for 25-30 minutes, or until the edges are golden brown and the center appears set.
Allow the bars to cool completely at room temperature, then refrigerate for at least 1 hour before slicing.
Lift the bars out of the pan using the edges of the parchment paper and cut into squares or rectangles.
Notes
For an extra touch of indulgence, drizzle with melted chocolate or butterscotch.