Nanaimo Bars

Method

1. mix8 min
   cocoa-egg mixture thickened over gentle heat
   Melt 1/2 cup butter with sugar and cocoa over barely simmering water. Whisk in the egg and stir until the mixture visibly thickens; gentle heat cooks the egg without scrambling it.
2. mix3 min
   crumb mixture evenly moistened
   Stir graham crumbs, coconut and walnuts into the warm cocoa mixture, then press firmly and evenly into an 8-inch square pan. Uneven compression produces crumbly corners.
3. rest25 min
   base cool and firm
   Chill the base until firm enough that the middle layer can be spread without dragging crumbs into it.
4. whisk5 min
   smooth pale filling
   Beat 1/2 cup softened butter with powdered sugar, custard powder and cream until smooth and spreadable. Spread in an even layer over the cold base.
5. rest25 min
   custard layer cold and set
   Chill again before adding chocolate. A warm middle layer causes the chocolate to sink and smear instead of forming a clean cap.
6. mix4 min
   thin glossy chocolate topping
   Melt chocolate with 2 tablespoons butter, cool just until no longer hot, and spread thinly over the filling.
7. rest20 min
   chocolate set but not rock-hard
   Chill until set, then cut with a warm dry knife before the chocolate becomes brittle enough to crack away from the filling.