Melt the butter using a microwave or double boiler. Let it cool to about 40°C (warm but not hot).

Preheat your oven to 175°C (top + bottom heat) for 10 minutes.

Chop chocolate into even 10g chunks. Prepare heat-stable chips for topping.

Crack 1 egg into a large bowl, add 50g of fine granulated sugar, then pour in the cooled, melted butter. Use a whisk to mix until completely combined into a smooth, liquid mixture.

Sift cake flour, cocoa powder, and baking powder directly into the bowl.

Use a silicone spatula to fold the mixture together gently—do not stir in circles or over-mix, as that can over-develop gluten.

Mix just until no dry flour remains. The dough should be soft, pliable, and non-sticky.

Divide the dough into equal 27g portions. Roll each into a smooth ball.

Flatten one dough ball into a small disc, place a chocolate chunk in the center, and wrap the dough around it. Seal tightly and reshape into a ball.

Gently press to form a thick disc about 1.5 cm tall.

Place onto a parchment-lined baking tray, leaving 3–4 cm between cookies.

Top each cookie with 5–6 chocolate chips, pressing lightly to secure.

Bake at 175°C for about 15 minutes, or until:

The edges are set

The tops look slightly dry

The centers feel soft to the touch

Remove from oven and cool on a rack for 5 minutes to allow cookies to set.

You'll get crisp edges, soft centers, and a perfectly molten chocolate core.