Preheat Oven & Make Base: Preheat your oven to 350°F (175°C). In a mixing bowl, use an electric mixer to beat together the ½ cup of butter and ½ cup of granulated sugar until creamy. Add the egg and vanilla and mix to combine. Stir in the graham cracker crumbs, coconut, and walnuts.
Bake Base Layer: Press the mixture evenly into the bottom of a 9×13-inch baking pan. Bake for 15-20 minutes, or until the bar layer is set and golden. Once baked, remove from the oven and set aside to cool completely.
Make & Spread Frosting: While the bars cool, make the frosting. In a new bowl, beat the ½ cup of butter until smooth. Gradually mix in the powdered sugar, followed by the milk, and then beat until the frosting is light and fluffy, about 2-3 minutes. Spread the frosting evenly over the cooled bars.
Add Chocolate Topping: To make the chocolate topping, microwave the chocolate chips and 2 tablespoons of butter in a microwave-safe bowl in 30-second intervals, stirring in between, until fully melted and smooth.
Finish & Serve: Smooth the melted chocolate over the frosting layer. Wait until the chocolate has set completely before slicing into squares.

To make spreading the chocolate easier, you can chill the frosted bars in the refrigerator for about 20-30 minutes before adding the chocolate layer.