Nanaimo Bars

Step 1

Line an 8-by-8-inch (20-by-20-centimeter) metal baking pan with parchment, allowing parchment to overhang by about 2 inches (5 centimeters) on two sides.

Step 2

Prepare the base: In a double boiler, or a heatproof bowl placed over a saucepan of boiling water, whisk butter with granulated sugar, egg, cocoa powder and vanilla until melted. Continue whisking until mixture thickens slightly, 1 to 2 minutes. Remove from heat.

Step 3

Stir in crumbs, coconut and nuts until the mixture is well combined and resembles wet sand.

Step 4

Transfer mixture to the parchment-lined pan and use your fingers to press it into an even layer. Transfer pan to the refrigerator to chill until firm, at least 15 minutes.

Step 5

Meanwhile, prepare the buttercream: In a stand mixer fitted with a paddle attachment, cream butter on medium speed for about 1 minute. Add heavy cream and custard powder and mix until combined, scraping sides and bottom of the work bowl as needed. Add 1 cup confectioners’ sugar and mix on low until incorporated. Add remaining confectioners’ sugar and mix on low until combined, scraping the bottom of the bowl as needed, then mix on medium-high speed until smooth, light and fluffy, 2 to 3 minutes.

Step 6

Remove pan from refrigerator. Dollop the buttercream on top of the base layer then gently spread it evenly on top using an offset spatula. Transfer pan to the refrigerator to chill until buttercream is set, about 30 minutes.

Step 7

Prepare the topping: In a small, heavy saucepan or a double boiler, heat the chocolate and butter over low, stirring often, until melted and evenly combined, 2 to 3 minutes. Remove from heat. Take pan from refrigerator and pour chocolate on top of buttercream layer. Working quickly and carefully, spread the chocolate evenly over the buttercream using an offset spatula. Sprinkle with flaky sea salt, if using.

Step 8

Return pan to refrigerator and chill until chocolate hardens, about 25 minutes.

Step 9

To serve the bars: Lift excess parchment to remove Nanaimo square from the pan. Cut into 16 2-inch (5-centimeter) squares. Store bars in the refrigerator until ready to serve. Bring to room temperature before serving. Store remaining bars in the refrigerator for a few days, or wrap well and freeze.