Remember to source organic, estate-grown chocolate whenever possible to get the biggest flavour and health benefits out of this sinfully simple dessert.
Preheat oven to 375 F (190 C). Grease and line the bottom of a 9-in (23-cm) pie pan with parchment paper.
Pulse chocolate chunks in a food processor with 1/4 cup (60 mL) sugar to grind finely but not melt. Whip remaining sugar with eggs, zest, and vanilla until pale and thick, about 5 minutes. Fold in chocolate, almonds, and melted butter just until combined. Pour into prepared pan and bake for 40 to 50 minutes, until a tester inserted in the centre of the cake comes out clean. Let cool completely in pan, then dust with icing sugar before slicing to serve.