To make the cake: Preheat the oven to 350 F (180 C). Grease and line a 6 or 4-inch cake tin with some oil (Alternatively, grease 2 large muffin cups).
In a large bowl whisk the egg whites whilst gradually pouring in the sugar until firm peaks form.
2 medium eggs, 66 g (1/3 cup) granulated sugar
In a medium bowl, mix together the egg yolks, salt, cocoa and vanilla.
2 medium eggs, pinch salt, 2 tbsp unsweetened cocoa powder, 1 tsp vanilla extract
In a small pot melt together the chocolate and butter over a low heat until melted. Pour this into the egg yolk mixture and whisk to combine. Slowly beat the boiling water into the chocolate mixture too.
66 g (2.3 oz) dark chocolate (70% cocoa solids), 66 g (4 ½ tbsp) unsalted butter, 60 ml (1/4) boiling water
Mix about 1/4 of the beaten egg whites into the yolk mixture to loosen it. Then pour the yolk mixture into the egg whites and gently fold together using a rubber spatula.
Pour cake mixture into the prepared tin and bake for 20-30 minutes, it should still be set and dry on top. (The 6" pan will need around 20-25 mins, muffin tins will need 15-20 mins). Leave to cool completely in the tin before turning out onto a plate.
Serve with the whipped cream and fresh pomegranate arils.