- Preheat your oven to 170ºC
- Combine the cake flour, baking powder and salt, sift into a large bowl (use a stand mixer, if you have one, with the paddle attachment) add the 250g caster sugar, mix to combine.
- Make a well in the centre of your flour combo, add the coffee, egg yolks, oil and vanilla bean seeds, mix until smooth.
- In another, extra large bowl, whisk the 7 egg whites until foamy, add the cream of tartar then mix until you have soft peaks (the cream of tartar is not essential, not an issue if you can't find it, but it does stabilise the egg whites) gradually add the additional 50g caster sugar, whisking until you have firm peaks and the sugar has dissolved.
- Fold the egg whites into the batter in three stages, you might need to carefully tip the batter into the egg whites after the first addition if your mixer bowl is not big enough.
- Pour the batter into an ungreased, unlined angel food cake tin and bake for 55-60 minutes.
- Remove the cake from the oven and immediately invert to cool, if your tin doesn't have "feet" find a bottle that fits inside the centre tube of the pan, invert the cake over the bottle and leave to cool.
- When completely cold, run a sharp knife around the inside and the centre section of the cake tin, remove the cake, still on the base of the tin, then run the knife between the bottom of the cake and the tin; invert the cake onto your serving plate.
- Slice giant slabs of cake with a serrated knife and enjoy!
- The cake will keep in an airtight container for 3 days at room temperature or up to a week in the fridge, tends to only last a couple of days in my house :)
Swiss meringue buttercream
- Combine the egg whites and sugar in a bowl, place over a pan of simmering water, don't let the bowl touch the water.
- Using a hand whisk, whisk constantly until the temperature reaches 72ºC.
- Transfer to a stand mixer and whisk on medium high until the mixtures cools, has doubled in size and forms stiff peaks.
- Change to the paddle attachment and add the butter a piece at a time, mixing to incorporate each piece, the mixture may look alarmingly curdled but keep mixing and it will magically come back together.
- Once all the butter is incorporated add the salt and vanilla bean seeds, mixing on slow until combined.
- Blend the coffee with 1 Tbsp boiling water, add to the cream and mix to combine.
- Tip the sugar into a small/medium heavy based pan and heat on a medium to high setting, stirring every now and then, until the sugar starts to melt.
- Continue to cook, swirling the pan occasionally, until the sugar has melted, turned a lovely caramel colour and has started to smoke; things can be a bit tricky here, you want to cook the caramel enough to develop that deep toasted flavour that offsets the sweetness, but it's a very fine line, leave it too long and it will burn and become inedibly bitter.
- As soon as you are happy with the caramel, whisk in the butter, take care, it will bubble and spit.
- Remove from the heat and whisk in the cream, if your caramel has formed clumps, return to the heat and stir until smooth.
- Add salt flakes, pour into a clean jar and leave to cool.
- Once cool, cover with the lid and store in the fridge, it will keep for 2 weeks.