Prepare the coffee and leave it to cool down a bit; for this recipe, it should be lukewarm.
First, separate the egg whites and yolks. Mix the coffee with the oil and the lemon zest, stirring with a whisk. Sift the flour with baking powder, sugar and vanilla extract to ensure the mixture stays light and fluffy. Whisk the egg whites for about 5 minutes, adding a pinch of salt, until the mixture forms stiff peaks.
After whisking the egg whites, add them into the mixture, folding in from bottom to top to prevent lumps from forming.
Take the chiffon cake cupcake moulds, butter them and pour in about 100 g (3.5 oz) of mixture per mould. The cupcakes are now ready for baking. Place them in the oven for 35 minutes at 150°C (300°F).