Preheat the oven to moderate (180°C/160°C fan-forced). Grease a deep 19cm square cake pan, line base and sides with baking paper.
2
Combine cocoa and the boiling water in a large bowl, stir until smooth. Add chocolate, butter, sugar and sifted flour, then almond meal; stir until combined. Stir in egg yolks, one at a time.
3
Beat egg whites in a clean, small bowl with an electric mixer until soft peaks form; fold into chocolate mixture in two batches. Pour mixture into prepared pan.
4
Bake in a moderate oven for about 1 hour 15 minutes or until firm to touch. Stand cake in pan for 5 minutes; turn top-side up onto a wire rack to cool.