Preheat the oven to 325F (160C).

Grease a tube pan.

In a small bowl, add the cocoa and boiling water and whisk until the mixture is smooth. Set aside to cool.

In a large mixing bowl, add the flour, sugar #1, baking powder and salt. Whisk together to combine.

Make a well in the centre. Add the oil, egg yolks and vanilla and whisk until the batter is smooth.

In the bowl of a stand mixer, add the egg whites and whisk on high speed until the whites are frothy.

Add the cream of tartar and continue to whisk on high until soft peaks form.

At soft peak stage, sprinkle in sugar #2 while the whites continue to whisk on high speed until stiff peaks are formed.

Using a rubber spatula, gently fold ½ of the egg whites into the chocolate batter.

Before the whites are fully folded in, add the remaining ½ egg whites and continue to fold in gently until the whites are just blended into the cake mixture.

Pour the batter into the tube pan. Gently tap the pan a few times to dislodge any air bubbles.

Bake for approximately 45-50 minutes until the cake springs back lightly when touched.

Immediately invert the pan and suspend it using something that allows the cake to be well above the kitchen counter.

Let the cake cool completely in the pan, approximately 1 & ½ hours.

When the cake has cooled, loosen the sides of the cake from the pan and invert onto a wire rack.

Reinvert onto a serving plate.

Dust with icing sugar.