Preheat the oven to 200C/180C Fan/Gas 6. Line a 2 lb loaf tin.
In a large bowl, or the bowl of a stand mixer, combine the flour, baking powder, baking soda, cocoa powder, sugar and salt.
Get the kettle on – essentially we are going to make a hot chocolate. Combine the boiling water, hot chocolate powder and milk in a mug. Set aside.
Make a well in the dry mix, and add the eggs, syrup and oil. Once thoroughly combined, slowly pour in the hot chocolate mixture until it has all been incorporated. The batter will be fairly thin.
Pour the batter into the tin and bake for 35-40 minutes, until a skewer inserted comes out clean. Let cool on a wire rack.
Once completely cool, make the frosting. Heat the oven to 220C/200C Fan/Gas 6.Add the egg whites to a large bowl/bowl of a stand mixer and whisk on high until soft peaks form. (If using a stand mixer, use a spatula to ensure all the liquid from the bottom has been whisked). Add the sugar in slowly - about a tbsp at a time until fully combined and stiff peaks are beginning to form. Spread this mixture over the cake and bake in the oven for about 3-5 minutes until brown on top in places.
Sprinkle over any chocolate and biscuit decorations before slicing and serving!