Featherweight sponge

This is the second times I practised to make this Sponge cake. I love the classic combination of homemade jam and cream. It just perfect.

INGREDIENTS
1/2 cup (75g) plain flour
1/2 cup (75g) cornflour
1/2 tsp cream of tartar
1/4 tsp bicarbonate of soda
4 eggs, separated
3/4 cup (165g) caster sugar
1/2 tsp vanilla extract
Blackberry jam
200ml thickened cream, whipped to soft peaks
Icing sugar, to dust

METHOD

1. Preheat oven to 180C. Grease two 20cm round cake pans.
2. Sift the plain flour, cornflour, cream of tartar and bicarbonate of soda into a large bowl. Sift twice more, then set aside.
3. In a clean, dry bowl, whisk the egg whites with electric beaters until soft peaks form. Gradually add the caster sugar, whisking constantly, until you have stiff peaks. Add the yolks, one at a time, and whisk until thick and pale.
4. Using a large metal spoon, fold in the vanilla extract. In 3 batches, gently fold in the dry ingredients until just combined.
5. Divide the mixture between the cake pans, then bake for 20-25 minutes or until the top spring back when lightly touched. Removed from the oven and cool in the pan for 5 minutes, then turn out onto a wire rack to cool completely.
6. Once cool, thickly spread the jam on top of one of the cakes, then top with whipped cream. Sandwich with the remaining cake, then dust with icing sugar and serve.