Prepare the Pan:

1. Line a 9×9-inch baking pan with parchment paper, leaving overhang on two sides for easy removal later. This is crucial for getting clean bars.

Make the Bottom Layer: 2. In a medium saucepan over low heat, melt 1/2 cup butter with sugar and cocoa powder, stirring constantly until smooth and well combined, about 3-4 minutes.

3. Remove from heat and quickly whisk in the beaten egg. Return to very low heat and stir constantly for 2-3 minutes until the mixture thickens slightly. This cooks the egg safely.
4. Remove from heat and stir in graham cracker crumbs, coconut, and walnuts until everything is evenly coated and combined.
5. Press the mixture firmly and evenly into the prepared pan using the back of a spoon or your hands (slightly dampened hands work great). The firmer you press, the better the bars will hold together.
6. Refrigerate for at least 15 minutes while you prepare the middle layer.

Make the Middle Layer: 7. In a mixing bowl, beat softened butter with an electric mixer on medium speed until fluffy, about 2 minutes.

8. Add heavy cream and custard powder, beating until combined.
9. Gradually add powdered sugar, one cup at a time, beating on low speed first then increasing to medium-high. Beat for 3-4 minutes until the mixture is light, fluffy, and smooth.
10. Spread the custard layer evenly over the chilled bottom layer using an offset spatula or butter knife. Take your time to create a smooth, even surface.
11. Refrigerate for at least 30 minutes until firm to the touch.

Make the Top Layer: 12. Create a double boiler by placing a heatproof bowl over a pot of simmering water (don’t let the bowl touch the water), or use a microwave-safe bowl.

13. Melt chocolate chips and 2 tablespoons butter together, stirring frequently until completely smooth. If using microwave, heat in 20-second intervals, stirring between each.
14. Let the chocolate mixture cool for 5 minutes—this prevents it from melting the custard layer beneath.
15. Pour the chocolate over the custard layer and spread evenly using a spatula. Work quickly but gently to avoid disturbing the layer underneath.
16. Refrigerate for at least 2 hours, or until the chocolate is completely set and firm.

Cut and Serve: 17. Using the parchment overhang, lift the entire bar out of the pan and place on a cutting board.

18. For clean cuts, use a large sharp knife dipped in hot water and wiped dry between each cut. Cut into 16-20 squares.
19. Let bars sit at room temperature for 5-10 minutes before serving for the best texture and flavor.