Preheat the oven to 160 degrees C and grease a 23cm springform cake tin. Dust tin with flour after greasing.
Sift together the flour, cocoa, baking powder, bicarb soda and salt. Add sugar and stir until blended. Add oil and mix a few seconds.
In a separate bowl, whisk the eggs until lightly beaten. Whisk in the milk and vanilla. Add this to the flour mixture and mix until well blended. Gradually add the boiling water and stir until just blended, then pour into the cake tin.