Prepare the outer dough by softening unsalted butter to room temperature. If unavailable, microwave for 10 seconds at a time until softened.

Cream the butter, then add sugar and milk sequentially, mixing well. Warm the milk slightly if cold to avoid separation.

Sift the flour into the mixture and combine into a dough.

Form the dough into a ball, wrap in plastic wrap, and refrigerate for 30 minutes.

Prepare the inner dough by softening unsalted butter and creaming it. Add sugar, milk, and melted dark chocolate sequentially, mixing thoroughly.

Sift flour and cocoa powder into the mixture and combine into a dough.

Add chocolate chunks to the dough and form into a ball. Wrap in plastic wrap and refrigerate for 30 minutes.

Divide the outer dough into 10 portions (approximately 20g each) and the inner dough into 10 portions (approximately 15g each).

Flatten each outer dough portion into a thin circle and wrap it around an inner dough portion. It's okay if the inner dough isn't fully covered.

Press the wrapped dough to a thickness of 0.7cm using a flat tool or your hands.