Step 1

Butter and line a 9×9″ square pan with parchment paper or aluminum foil, leaving an overhang on two sides for easy removal. Set aside.

Step 2

Melt the butter in a large heatproof bowl over a saucepan of very gently simmering water. Whisk in the sugar, cocoa powder, and salt. Remove from heat and slowly add in the egg while whisking vigorously. Return to heat and cook for 1-2 more minutes until the mixture is smooth and resembles hot fudge.

Step 3

Add in the graham cracker crumbs, shredded coconut, and chopped nuts.

Step 4

Stir until well combined. The mixture might appear dry at first, but keep mixing and it will come together.

Step 5

Transfer the mixture to the prepared pan. Press it firmly and evenly into the bottom of the pan and place in the fridge to chill while preparing the next layer.

Step 6

In a large mixing bowl, beat the butter, custard powder, and vanilla until combined. Mix in 1 cup of powdered sugar along with 1 tablespoon of cream at a time, mixing in between until smooth. Add 1-2 more teaspoons of cream, ONLY if needed, to reach a thick and spreadable consistency.

Step 7

Spread the buttercream evenly on top of the base layer using an offset spatula. Place in the freezer for 10-15 minutes to firm up while preparing the next layer.

Step 8

Melt the chocolate with the cream in a medium heatproof bowl over a saucepan of very gently simmering water, stirring frequently, until completely melted and smooth.

Step 9

Pour over the cold buttercream and quickly spread it all over using an offset spatula. Place back in the fridge until ready to cut into squares. See expert tips on how to cut below.