[Preparation]
Cut milk chocolate into small pieces. Put the milk chocolate and milk in a heat-resistant container, warm it in a microwave at 600W for 20-30 seconds, and stir to dissolve the chocolate until smooth. Set it aside to cool down.
Preheat an oven to 200℃ / 392 F.
Stir well flour, cocoa, and baking powder, and set aside.

[Cake Batter]
Cream unsalted butter until soft and smooth. Add granulated sugar in 2 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 5 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.
Note: Please use eggs at room temperature to prevent the batter from separating. Warm it up a little in a hot water bath before adding it if it's cold.

Add ground almonds and use a spatula to mix until smooth while crushing lumps.
Add half of the prepared chocolate milk and mix well until smooth. Make sure the chocolate milk has cooled down to room temperature before adding it.

Sift half of the dry ingredients (flour, cocoa, and baking powder) over the mixture and fold it 10 times. Add the remaining chocolate milk and 50g milk, and fold it 10 times.

Sift the remaining dry ingredients over the mixture and fold it until you don’t see flour left.
Add chocolate chips and fold roughly 10 times.

Put the batter in glassine-paper-lined muffin pan cups. Top with chocolate chips for topping around the middle and press lightly.

[Bake]
Lower the oven to 180 ℃ / 356 F and bake for 25-28 minutes. Remove from the oven, and cool down for 5 minutes. Remove it from the pan and let it cool on a rack.

When freshly baked, the outside is crunchy and the inside is fluffy and moist. If you don't eat it right away, wrap it with cling wrap while it's slightly warm.
Store them at room temperature with wrapping. Best eaten within 3-4 days.