Nanaimo Slice

5 from 2 votes

A popular tray bake from Canada, Nanaimo Slice is a sweet chocolatey treat, with a nutty-coconut base and a custard buttercream filling.

Course: Dessert, Snack

Cuisine: Canadian

Keyword: Chocolate, Coconut, Tray Bake, Walnuts

Servings: slices

Line a 9x12 inch tray with greaseproof paper and set aside.
In a medium-large pan, melt the margarine/butter, soft light brown sugar, and cocoa powder over a low heat. Meanwhile, crush the digestive biscuits, either by pulsing in a blender or placing them in a freezer bag and hitting with a rolling pin.
Once the margarine/butter, sugar & cocoa powder have melted, add the crushed digestives, desiccated coconut & walnuts, and mix until combined. Add the beaten egg and mix through.
Transfer the base mixture to your pre-lined tray, and press evenly & into the corners of the tray with the back of a spoon. Leave to cool before transferring to the fridge to set, ideally for a couple of hours.

In a large bowl, sift the icing sugar and custard powder, before adding the margarine/butter and double cream Beat together until light and fluffy.
Remove the base from the fridge and spread the custard icing evenly across the top, right into the corners. Return to the fridge whilst you prepare the topping.

Melt the dark chocolate over a bain-marie or in short bursts in the microwave. Add the margarine/butter and stir until melted through.
Pour the chocolate mixture over the filling, spread it evenly & right into the corners. Place back into the fridge to set, ideally for a couple of hours.
When ready to serve, cut the Nanaimo Slice into bars, ideally whilst still in the tray. If it isn't possible to cut in the tray, at least score the chocolate in the tray, to avoid the filling pressing out whilst cutting.

Birds Custard Powder is a staple in UK homes, but I know it isn't available everywhere.
A good substitution is actually some Vanilla Jello Powder!
Alternatively, you can just use some corn flour (corn starch), and add a little vanilla extract for the custard-like flavour. And for the full custard-powder-effect, you could even add a smidgen of yellow food colouring - although that's purely optional!