Method

• 1.
  Preheat oven to 170°C/150°C fan-forced. Find a sturdy glass bottle that will fit inside the inner tube of the angel food cake pan. Do not grease pan.
• 2.
  Place the cocoa, coffee and 170ml boiling water in a large bowl and whisk to combine. Set aside.
• 3.
  Place caster sugar in a medium bowl and scoop out 2 tbs to reserve for the egg whites. Add flour and ½ tsp fine salt to the larger amount of sugar and set aside.
• 4.
  In a stand mixer fitted with the whisk attachment, whisk the egg whites and cream of tartar for 3 minutes, or until stiff peaks. Add reserved 2 tbs sugar in two batches, whisking for 30 seconds after each addition.
• 5.
  While whisking whites, add yolks and oil to cocoa mixture and whisk until smooth. Sift flour mixture over and whisk until combined and smooth.
• 6.
  Gently fold in one-third of meringue, then fold in remaining meringue until no white streaks remain. Spoon mixture into pan. Bake for 1 hour and 5 minutes, or until puffed and cake around inner tube feels dry and springy. This is important – if the cake is under-baked, it can drop out of the pan when inverted. Invert pan immediately onto the sturdy glass bottle and let stand for 3 hours, inverted, to cool completely (see recipe notes).
• 7.
  Using a sharp thin knife, saw around pan edge and inner tube to release cake onto a serving plate, then use a butter knife or offset spatula to gently ease the base plate off the cake.
• 8.
  For the mascarpone cream, stir all ingredients in a large bowl until well combined (mixture will thicken as you stir; there should be soft billows, yet it should hold its shape). Using one-third of the mascarpone cream, cover entire surface of cake, including down centre (this will set the crumb). Chill cake and remaining mascarpone cream for 15 minutes.
• 9.
  Smooth remaining mascarpone cream all over to neatly cover the cake, then chill while you make the chocolate swipe.
• 10.
  For the chocolate marble swipe, melt all ingredients in a medium bowl over a saucepan of boiling water (don’t let base of bowl touch the water). Set aside for 5 minutes until lukewarm but still runny.
• 11.
  With an offset spatula, swipe the chocolate lightly on top of mascarpone cream to create a marbled white and brown appearance (you won’t use all of it). Cut into slices to serve.