In a bowl, sift together cake flour, salt, sugar and baking powder. Stir in water, egg yolks, vanilla and oil. Set aside.
In a mixer bowl, whip egg whites with cream of tartar. Once foamy gradually add in other ½ cup of sugar. Continue whipping until it forms stiff peaks.
Carefully fold whipped egg whites to the cake batter until it is well incorporated. Do not overmix.
Pour into prepared mammon molds.
Bake in the 350F preheated oven for 20-25 minutes.
Brush with softened butter and sprinkle with sugar. Serve.