Preheat the oven to 320 degrees F.

Sift the flour into a large bowl, add 1 cup sugar, baking powder and salt. Add egg yolks, oil, water and vanilla. Beat with a whisk until pale and smooth. 

In a stand mixer, beat egg whites on medium speed until soft peaks form, about 4 minutes. Add the cream of tartar and the remaining ½ cup of caster sugar. Beat until stiff peaks form, about 3 minutes more.

Slowly pour the batter into the egg whites and carefully fold with a spatula until well combined. Pour the batter into an ungreased chiffon cake tin. Carefully smooth the top and lightly bang the pan on the counter once.

Put the cake into the oven on 320 and bake for 50 minutes. After this time, increase the heat to 350 degrees and bake for an additional 5-10 minutes until the top becomes golden brown and slightly rises above the top of the pan. Be sure not to open the oven door during this time to prevent the cake from deflating.

Remove the cake pan from the oven and invert to cool completely. If your pan has legs, this will do. Otherwise, place a bottle into the center of the chiffon tube and allow the cake to hang upside down.

Once completely cool, slide a long spatula down the side of the pan and then slowly slide around the pan to separate the cake. Use the same method to separate cake from the funnel and base of the tin.

To serve, dust the cake with powdered sugar and fill the center with fresh berries. Serve alongside cold whipped cream.