• Line an 8x8 or 9x9 inch pan with parchment paper (or lightly greased aluminum foil) leaving an overhang around the edges.

Base Layer

• Add about 1-2 cm (½ -1 inch) of water to the bottom of a medium saucepan over low heat. Place a glass bowl on top so that the bottom of the bowl doesn't touch the water.
• Add the butter, sugar, and cocoa powder to the glass bowl. Melt the ingredients together while stirring occasionally.
• Once completely melted, add in the egg while whisking constantly. Whisk the mixture until thick, glossy and smooth.
• Carefully remove the bowl from the heat and stir in the graham crumbs, coconut and chopped walnuts.
• Press the mixture into the bottom of the prepared pan and place in the freezer to firm up for 20 minutes as you make the filling.

Middle Layer

• In a large bowl, beat the butter until soft and fluffy.
• Mix in the custard powder and cream.
• Slowly beat the powdered sugar in a little at a time - until it's very thick (thicker than normal frosting).
• Spread the custard buttercream over the base layer, and place in the fridge for at least 15 minutes to firm up.

Chocolate Layer

• Add the chocolate to a large heat proof bowl.
• Microwave on medium power (not high - otherwise it won't melt properly) for 45 seconds. Remove from the microwave and stir. (Or melt using a double boiler).
• Repeat the process until the chocolate is melted.
• Stir in the oil.
• Pour the mixture over the bars and smooth the top.
• Place in the fridge to firm up.

Cutting the Bars

• Once the chocolate is about 75% hardened (after 20 minutes or so in the fridge), score the bars by lightly tracing lines through the chocolate where you'll cut the bars.
• Return to the fridge until completely firm.
• When the chocolate is fully hardened, take the bars out of the fridge for 10 minutes to warm up for easier slicing. Then cut into bars along the lines that you scored in the chocolate.
• Enjoy bars cold from the fridge, or at room temperature (they'll take 10-15 minutes to warm up).