Separate 4 eggs into yolks and whites, and let them come to room temperature. Place an oven rack in the middle position and preheat the oven to 325 degrees F (165 C). Line just the bottom of a 9" x 5" x 3" loaf pan with parchment paper. Do not grease the sides of the pan or the parchment paper, as we need the cake to stick to the sides of the pan as it rises. Soak 1 cake strip in cold water for 5 minutes. Then shake off excess water but do not wring. And place the soaked cake strip around the loaf pan. To help hold up this cold moist cake strip, wrap a band of aluminum foil over it, tucking it under the pan so that the walls of the pan are surrounded.

In a large bowl, sift together 1 cup of cake flour, 2 tsp baking powder, 1/3 cup granulated sugar, and 1/2 teaspoon salt. Whisk to combine. Then add 4 egg yolks, 1/3 cup vegetable oil, 1/2 cup of water, 1/4 tsp of finely grated orange zest, and 2 tsp of vanilla extract. Beat with an electric mixer or by hand just until smooth or well blended.

In the bowl of your stand mixer with the whisk attachment, beat together 4 egg whites and 1/2 tsp cream of tartar on medium speed until frothy, about 1 minute. Increase the speed to medium-high, and very slowly add in 1/3 cup sugar. When all the sugar is added, increase the speed to high and continue beating until stiff peaks are formed. Ensure the meringue forms stiff peaks so that it is not under-beaten. Under-beating the meringue will result in the chiffon loaf collapsing after baking. One third at a time, fold this meringue mixture into the batter mixture until well combined. Transfer this batter into the prepared loaf pan. Gently jiggle the pan back and forth to spread the batter evenly and smoothen the top surface as much as possible. Then tap it gently on the counter to remove any large air pockets.

Bake in the preheated oven at 325 F (165 C) for about 70 to 75 minutes or until the loaf is golden brown, the surface springs back when touched lightly at the center, and a toothpick inserted in the center comes out clean. Immediately invert the pan onto 2 mugs of the same height, and let the loaf cool in the pan upside-down completely to room temperature. The loaf will have risen higher than the sides of the loaf pan, so it's necessary to invert the loaf pan balanced over 2 mugs, rather than a metal rack.

When it has cooled completely to room temperature (while in the loaf pan, upside-down), turn the loaf pan right-side up again and run a knife along the 4 edges of the cake. Gently tip the loaf pan sideways to unmold the cake onto a clean surface or chopping board, carefully peel off the parchment paper the cake was baked with, then flip the cake right-side up onto a serving dish.

Melt 2 tbsp of unsalted butter, and brush the top of the taisan loaf with the melted butter.

The taisan loaf will keep in an airtight container at room temperature for 1 to 2 days, or in the fridge for 3 to 4 days. If stored in the fridge, let it come to room temperature before serving. Enjoy!