Beat egg yolks and sugar with a hand whisk until slight pale. Add oil, mix well followed by blueberry puree and combine well.
Sift the flour for the second time directly into the yolk mixture together with the lemon zest. Stir as you add till smooth and egg mixtures into thick paste.
Meringue - Beat egg whites and lemon juice until frothy. Add sugar in 2 batches and whisk until stiff peak and glossy-looked
Fold ⅓ of egg whites into the yolk mixture with a rubber spatula. Then pour in the remaining egg whites in 2 separate rounds, gently fold before the next until just combined.
Pour batter into a 20 cm ungreased chiffon tube pan and bake in preheated oven at 160 deg C for 10 minutes. Then lower temperature to 150 deg C and bake for another 40 minutes.
Remove from oven, invert cake immediately on a wire rack to cool completely before unmoulding.