• Grease two swiss roll tins (23 x 33 x 2-3cm) and line with baking paper.
• Pre-heat oven to moderate (180 degrees celsius).
• Beat egg whites until stiff.
• Add sugar gradually, continuing to beat between each addition.
• Whisk egg yolks together with the warm water.
• Add egg yolks to mixture and beat again until well combined.
• Sift flour together with baking powder and salt. Fold into mixture gradually until combined.
• Add half of the mixture to each tin and smooth out to edges.
• Bake for 10-12 minutes.
• Allow cakes to cool in tin for 10 minutes.

Rolling and filling

• Sprinkle two sheets of baking paper (slightly larger than the swiss roll tins) with caster sugar.
• Carefully flip the warm sponge onto the baking paper sheets (and peel away the baking paper the sponges were cooked in).
• Use the baking paper to roll the sponges up firmly and leave to cool completely.
• When the sponges are cool, unroll gently. Spread the jam or cream (or both) filling evenly over the surface of the sponge, leaving a gap of about 5 cm at one end. Slowly roll the sponges up again.
• Serve with the open edges on the bottom to keep the sponges tightly rolled. Dust with icing sugar.