Preheat oven to 180C
Grease a swiss roll tin (30cm x 25cm x 2cm deep) and line base with baking paper, allowing a 3cm overhang on the long sides of the tin.
Sift the combined flours and baking powder three times and set aside.
Using electric mixer, beat the egg whites and salt until soft peaks form, then gradually add the sugar, beating constantly until soft peaks form.
Add the egg yolks and vanilla. Beat until combined.
Gently fold in the flour mixture and spread evenly into the tin. Bake for 15 mins, until cake springs back to gentle touch in centre.
Meanwhile, lay out another sheet of baking paper and sprinkle with icing sugar and coconut.
When cooked, turn sponge out onto baking paper; spread quickly with jam and then roll up, starting at the short end.
Leave to cool for around 15-20 mins. Slice and serve.