1¾ cups plain flour
1/3 cup cornflour
1 Tbsp baking powder
½ tsp salt
1¼ cups caster sugar, plus ¼ cup extra
6 eggs separated, plus 1 extra egg-white
2 oranges, grated zest, plus ¾ cup juice, plus extra zest to serve
½ cup vegetable oil
1 tsp vanilla extract
½ tsp cream of tartar
1½ cups icing-sugar mixture
20g butter, melted
1-2 Tbsp lemon juice
Preheat oven to moderate, 180°C. Line base of 22cm angel-cake pan (see cook's tip) with baking paper.
Sift combined flours, baking powder and salt into a large bowl. Stir in sugar. Make well in centre.
In a jug, whisk yolks, juice, zest, oil and vanilla together. Lightly stir into flour mixture.
In a large bowl, using an electric mixer, beat all egg-whites until foamy. Add cream of tartar and beat until soft peaks form. Gradually add extra sugar, beating until stiff, until glossy peaks form.
Lightly fold egg-white mixture into batter until combined. Pour into ungreased angel-cake pan.
Bake 50-60 minutes, until cooked. Invert cake onto a rack - leave in pan. Cool 1½ hours, until cold.
Line a wire rack with baking paper. To remove from the pan, run a butter knife or metal spatula around the outside and inside edges. Invert onto rack.
To make the icing, sift icing-sugar mixture into a large bowl. Stir in butter and enough juice to make a runny consistency. Pour over cake. Sprinkle with extra zest.