1. Preheat oven at 160°C/320°F.

2. Cut the butter into chunks to speed up the softening and add into a large bowl.

3. Separate the eggs.

4. In the bowl of softened butter, add sugar. Mix on high speed for about 3-4 minutes. In between add milk and vanilla extract. Continue mixing on high speed until creamy, fluffy and pale.

5. Add in the egg yolks, one at a time. Mix until the yolk disappear before adding another.

6. Sift in the dry ingredients (flour and baking powder). Use a spatula to fold in just until the flour disappear, do not over mix. Set aside while working on the egg whites.

7. Add cream of tartar into the bowl of egg whites. Mix on low speed for few seconds until foamy. Add in the sugar in 3 batches. Continue to mix on high speed until stiff peaks formed.

8. Fold the egg whites into the yolk batter in 3 batches. Fold just until the whites disappear, then add in another batch. You might find that the batter a little curdling, just keep adding and folding in the whites. Fold until it’s incorporated.

9. Transfer the batter into 9x3x3-inch pan, greased and lined with parchment paper.

10. Tap the pan on the table a few times to release air bubbles.

11. Bake in preheated oven at 160°C/320°F for 55-60 min or until the inserted skewer comes out clean.

12. Remove the cake from the pan to let it cool completely before cutting.

Remark: I made 2 versions, one with using cake flour and the other using regular or all-purpose flour. Both versions are light, soft and fluffy, especially for the one using cake flour. Although the one with all-purpose flour is slightly heavier but still has a different softness and fluffiness. Both turned out pretty amazing, like I said they reminded me of a Castella cake