Nanaimo bars are a classic Canadian sweet treat any time of year, but for Halloween you can give them a playfully spooky flair. Adding pumpkin pie spice and orange colour to the filling, over a chocolate base made using black cocoa powder and pretzel pieces instead of nuts (so everyone can enjoy) really suit the season. The melted marshmallow spiderwebs décor is easy AND eerie.
Nanaimo bars will keep in an airtight container in the fridge for up to 1 week.
Lightly grease a 9-inch square pan and line it with parchment paper so that it comes up the sides.
For the crust, place the butter, sugar, cocoa powder and salt in a metal bowl and set over a pot of gently simmering water, whisking until the butter has melted. Add the lightly beaten egg and whisk until the mixture thickens to the consistency of pudding, about 1 minute. Remove the bowl from the heat and stir in the graham cracker crumbs and pretzel pieces. Scrape the crust mixture into the pan and spread to level it. Chill the pan while preparing the filling.
For the filling, beat the butter with 1 cup (130 g) icing sugar until smooth. Stir the custard powder, pumpkin pie spice, and salt with the milk and stir into the butter mixture until smooth. Beat in the remaining 1 cup (130 g) icing sugar. Do not overbeat—the filling should be smooth but not fluffy. Spread evenly over the crust. Chill while preparing the topping.
For the topping, melt the chocolate and butter in a metal bowl placed over a pot of barely simmering water, stirring gently with a spatula until melted. Cool the chocolate slightly and then pour over the filling, spreading to cover it. Chill the pan for about 2 hours before decorating.
Take the Nanaimo bars out of the pan and remove the parchment paper. You can add the decor before or after portioning into bars.
Melt the marshmallows in the microwave, stirring until smooth. Alternatively, the marshmallows can be melted in a small saucepot over low heat, stirring until smooth. Using gloved hands (this part gets VERY sticky), dip your fingers into melted marshmallows, pinch your fingers together and then spread them out – this will create a spiderweb effect between your fingers. Drape the webbing over the Nanaimo bars and repeat until you cover the surface of the bars. If you haven’t already, portion the bars and then top with candy corn.