A Canadian classic, these nanaimo bars are creamy, smooth, and melt in your mouth.
Line an 8x8 baking dish with parchment paper. You will make this in layers, and refrigerate each layer for at least 1 hour.
To make the base, boil a pan of water, and place a heat-proof bowl on top for a double-boiler. Once the water is boiling, turn it down to a simmer. Add the butter, sugar and cocoa powder, vanilla and egg to the bowl. Whisk the ingredients together, and once the mixture is smooth and has thickened (2 mins), remove from the heat, and mix in the coconut, walnuts and graham cracker crumbs.
Press the mixture into the bottom of the lined pan, and refrigerate for 1 hour.
For the filling, in a large mixing bowl, cream together the butter and the custard powder. Slowly add in the icing sugar, and add milk 1 tbsp at a time, until the mixture is smooth and creamy and spreadable. Spread the filling over the base layer, and place back in the fridge for another hour.
To make the top layer, add the chocolate and butter into a heat proof bowl, and microwave in 30-second intervals, stirring every time, until the chocolate is melted. You could also use a double-boiler for this too. Once the chocolate is melted, spread on top of the middle layer, and refrigerate for 30 minutes, or until you're ready to serve.
Lift the square out of the pan, place on a cutting board, and slice up into squares. Some of the chocolate may break, but don't worry, it'll still be delicious! Store in an airtight container in the fridge for up to one week.