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Separate the egg whites from the yolks into two large bowls. 
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Whisk the egg yolks with vanilla and caster sugar until thick, creamy and pale. 
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Sift the gluten free flour, baking powder and melted margarine into the yolks and whisk until combined. 
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Whisk the egg white to stiff peaks, put a spoonful into the yolks and fold in, this just loosens the mix. Fold the remaining whites into the yolk mix. 
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Grease and line a 9" by 11" swiss roll tin and pour in the mixture, place in oven preheated to gas mark 4/180c and bake for 15-17 minutes until golden and springs back when touched. 
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Allow to cool for 5 mins then tip onto another piece of greaseproof paper, starting from one of the shorter edges roll up tightly in the greaseproof and allow to go completely cold. 
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Once cold gently unroll (rolling while hot helps prevent the cake from cracking) and spread jam over the sponge before rerolling again. Slice and eat! 

