Taken from Jo Seagar's "It's Easier Than You Think" cookbook. Make sure the corn flour (corn starch) isn't wheaten. Also check the icing sugar is made from pure sugar, and doesn't contain cornstarch or gluten.
Preheat oven to 180C (350F). Coat 2 spring form pans with baking spray, then line with baking paper. The baking spray helps keep the paper from moving around.
In a microwave bowl or small saucepan, place the sugar and water. Bring to a boil. Stir every now and then to dissolve the sugar.
Beat the egg whites with an electric mixer until stiff. Slowly drizzle in the hot sugar mixture with the mixer running. Then beat really hard for 3 minutes. Mix in egg yolks and vanilla.
Sift together cornstarch, baking powder and salt. Carefully fold these into the egg mixture. Pour into prepared pans.
Bake 18-20 minutes. As soon as you remove them from the oven, drop the pans from knee height, square on the floor - seriously! This is a strange sponge making trick that 'shocks' the cake and stops it from deflating.
Then immediatly turn sponges out onto a wire rack or baking paper to cool upside down.
Beat cream and vanilla until soft peaks form. Warm jam for a few seconds in the microwave.
Place one sponge on the serving plate. Spread first with jam, then whipped cream.Top with strawberry slices. Then put second sponge on top. Dust with icing .