Rich, no-bake Nanaimo bars with a chocolate-coconut base, custard center, and chocolate top are a beloved family treat. These Canadian-American layered bars are an irresistible, freezer-friendly dessert.
Line an 8-inch square baking pan with parchment, leaving some overhang for easy removal.
Melt 1/2 cup butter in a medium saucepan over low heat, then stir in cocoa powder and 1/4 cup sugar until fully blended. Remove from heat and allow to cool slightly.
Quickly whisk in the beaten egg, stirring constantly; return to low heat and cook, stirring, until the mixture slightly thickens, about 1 minute. Remove from heat.
Stir in graham cracker crumbs, coconut, and walnuts. Press this mixture into the prepared pan, creating an even, compact base. Refrigerate for at least 30 minutes to set.
For the custard layer, beat together 1/2 cup butter, custard powder, 2 tbsp milk, vanilla extract, and powdered sugar until smooth and fluffy. Spread evenly over the chilled base and return to the fridge to chill for another 30 minutes.
For the top layer, melt chocolate chips with 2 tbsp butter over low heat, stirring constantly until just melted. Let cool slightly before pouring over the custard layer. Spread gently for a smooth finish.
Refrigerate bars for at least 30 minutes, or until chocolate is firm. Lift bars out, using parchment, and cut into squares with a sharp, warm knife for clean edges.