Step 1

Preheat oven to 250°F/121°C.

Step 2

Line a piece of parchment paper at the bottom of the 6" round cake pan.

Step 3

Separate the egg whites from egg yolks (while cold).

Step 4

Sift cake flour into a medium mixing bowl. Set aside.

Step 5

Pour 30ml oil in a small pot and heat until the oil reaches 75°-80°C.

Step 6

Add the flour mixture into the hot oil and mix well with a spatula.

Step 7

Pour cold milk and vanilla extract into the flour mixture to reduce the temperature and mix well.

Step 8

Add all the egg yolks in at once, and mix until very smooth. Set aside.

Step 9

Place the egg whites in a stand mixer fitted with whisk attachment.

Step 10

Whip egg whites, and add in cream of tartar when it becomes foamy.

Step 11

Gradually add in sugar and whip until soft peaks.

Step 12

Fold in egg whites into the yolk flour mixture in 3 batches, until well combined with no white streaks.

Step 13

Pour cake batter at a height of 8-10" to break any air bubbles, and into the baking pan/baking tray.

Step 14

Tap the pan a few times on the counter to release any remaining bubbles.

Step 15

Place cake pan into an aluminum foil dish/baking pan and place into a roasting pan in the centre of the oven.

Step 16

Pour in body temperature tap water (35°C) into the roasting pan to 1/2" deep.

Step 17

Bake the castella cake at 250°F/121°C for 60 minutes.

Step 18

Reduce the oven temperature to 300°F/149°C and bake for an additional 15 minutes.

Step 19

Test for doneness by gently tapping on the cake with a silicone spatula. If it feels springy, it is done. If not, extend the time for 5 more minutes.

Step 20

Turn off heat.

Step 21

Remove water bath and leave cake in the oven for another 5 minutes to dry up.

Step 22

Take the cake out of the oven and cool on a wire rack for 10 minutes.

Step 23

Give the cake a good tap around the edges to loosen.

Step 24

Remove bottom from the pan and cool completely on a rack.

Step 25

Cover and chill the cake or slice and serve.