[Preparation]
Preheat an oven to 190℃ / 374 F.
Brush the loaf pans with butter, sprinkle with bread flour, and knock off the excess flour. Let it sit in a fridge.

Let a small amount of softened butter put in a piping bag.
This is to draw a line on the top of the cake batter with butter after transferring it to the pans, but you can omit it. By drawing a line, the cake will crack easily and be baked well inside.

Put flour and baking powder for plain cake in a small bowl; set aside. Put flour, cocoa, and baking powder for cocoa cake in another bowl; set aside.

[Cake Batter]
Cream unsalted butter until soft and smooth. Add granulated sugar in 3 batches and mix well each time.
Use an electric hand mixer to beat it for 4-5 minutes on low speed until whitish. Scrape down the sides of the bowl from time to time.

Add beaten egg in 7-8 batches, and beat it on low speed until completely smooth each time. Finally, scrape down the sides of the bowl and mix again. It should look like a smooth buttercream.

Add vanilla bean paste and mix well. Add ground almonds and use a spatula to mix until smooth while crushing lumps.

[Plain Batter and Cocoa Batter]
Weigh it and divide it in half. The weight of one is around 285 - 300g / 10 - 10.6 oz. Sift dry ingredients for the plain cake (flour and baking powder) over half of the batter.

Use a spatula to fold until you don’t see any flour left. Put a small amount of the batter in the cake pan, and flatten it.

Add chocolate chips to the remaining batter and fold roughly. Put it in the pan, flatten it, and drop the pan lightly to fill the gaps.

Make the cocoa batter in the same way as plain. Draw a butter line on the top of each to crack easily.

[Bake]
Lower the oven to 170 ℃ / 338 F and bake for 45-50 minutes. Remove from the oven, and immediately drop the pan lightly 2-3 times to prevent shrinkage.

Cool down for 15 minutes, turn over the pan to remove the cake from the pan, and double-wrap each with plastic wrap while it's warm.
Let it sit at room temperature overnight to harmonize the taste. It's outside crunchy a little, inside soft.

Store them at room temperature with wrapping. Best eaten within five days.