A light pandan chiffon cake that is airy, soft and moist.
Preheat oven to 350 F. In a medium bowl, combine flour, salt and baking powder. In the bowl of a stand mixer, whisk the egg whites on medium-high speed until frothy. Add the cream of tartar and continue to whisk until egg whites form soft peaks. Gradually add 1/2 cup sugar while the mixer is running and continue beating until the egg whites form firm peaks that hold its shape when the whisk is lifted.
Meanwhile in another bowl, beat the egg yolks in a bowl until it is slightly thicker. Add the remaining 1 cup sugar and mix until incorporated. Add water, oil and pandan extract and mix well.
Add flour mixture gradually and mix until the batter is smooth. Gently fold the egg whites to the yolk batter in three additions until batter is uniform. Pour batter into a prepared 10 inch tube pan. Bake for 60-65 minutes, or until a toothpick inserted in the middle of the cake comes out clean. Invert cake on top of an overturned mug and let cool.
To unmold cake, loosen sides and bottom with a knife. Using your hands, gently push the cake away and downwards from the pan. remove gently and invert to a serving plate.
Combine melted butter and icing sugar until smooth. Add the pandan extract and stir until incorporated. If icing becomes too thick, add evaporated milk one tablespoon at a time to adjust consistency. It should be spreadable but not too thick. Spread on top of the cake and serve.
Icing may be curdly but taste won't be affected.