Preheat your oven to 180°C fan / 200°C. Lightly grease your Swiss roll tin and line with non-stick baking paper.
Separate your eggs into two small bowls - egg whites in one and yolks in the other.
In a large mixing bowl, add your egg yolks and half the caster sugar (50g). Whisk together until combined, then add your orange extract, milk and oil and whisk once more. Sift in the flour, cocoa powder and xanthan gum, and mix in until well combined, thick and glossy.
In a separate bowl, whisk your egg whites (using an electric hand whisk or stand mixer ideally) until they start to turn white and frothy. Gradually add the remaining caster sugar (50g), whisking until you have medium peaks.
In three stages, add your egg white mixture to your egg yolk mixture, folding it in carefully between each addition using a silicone spatula. Once all the egg white mixture is fully folded in, pour your mixture into your prepared tin. Spread it out gently to make sure it’s nice and even and bake in the oven for 10–12 minutes until cooked through.
Place a piece of non-stick baking paper on your work surface and dust it with the icing sugar.
While your sponge is still warm, loosen it from the tin and flip it out onto the baking paper. Peel off the baking paper on top that once lined the tin – don’t worry if you lose the outer layer of the cake because it sticks to the paper as you peel it off, that’s totally normal. Using your baking paper, roll the sponge up from the short end – the paper should be inside it as you roll. Try to roll fairly tightly, then leave the sponge to cool fully while rolled up. I prop something up against it to stop it from unrolling itself.