Combine dry ingredients - To a medium sized mixing bowl, whisk together the cake flour, baking powder and salt. Set aside.
Make meringue - To a separate large bowl add the egg whites and cream of tartar. Use an electric hand beater to whisk until frothy. Slowly add 1/2 (105g) of the sugar while the mixer is on high speed. Once all the sugar has been added continue mixing for 90 seconds. The mixture will thicken and become glossy. Take care not to overwhip the mixture otherwise it will result in large air bubbles in your cake.
Whisk egg yolks and sugar - To a separate bowl, add the egg yolks, remaining sugar (105g), water, and vanilla extract and use your electric hand mixer to whip until pale, thickened, and creamy, about 5 minutes. The mixture should fall off in ribbons when you lift the beaters.
Fold in dry ingredients - Sift 1/2 of the dry ingredients into the egg yolk mixture and use a spatula to fold through. Then add the remaining dry ingredients and fold through until no dry ingredients are showing. Take care not to overmix.
Fold in meringue - Add half the meringue and gently fold through with a spatula. Then add the other half and repeat.
Bake - Divide the mixture between the two cake 8-inch tins and bake in the middle rack of your oven for 30 minutes or until a toothpick inserted into the centre comes out clean. Once baked, allow to cool in the tins for 10 minutes before carefully running a knife around the sides to release them. Transfer to a cooling rack to cool completely.
Trim the cakes - Use a cake lever or large serrated knife to trim each cake into 2, giving you 4 layers all up.