Melt white chocolate and dark chocolate separately in two double boilers (water baths), each with 25g coconut fat. Heat on low, stirring occasionally, ensuring the water stays below a boil and does not splash into the chocolate (roughly 5-10 minutes).
While chocolate melts, line a small loaf pan with cling film. Mix milk and amaretto together in a bowl.
Drip a thin layer of melted dark chocolate into the bottom of the lined loaf pan.
Dip butter biscuits into the amaretto mixture for 1-2 seconds, then carefully layer them over the dark chocolate. Cover with another layer of dark chocolate.
Refrigerate for 5 minutes.
Dip more biscuits in the amaretto mixture and layer them in the pan. Cover with dark chocolate and refrigerate for 5 minutes.
Switch to white chocolate: layer white chocolate, add dipped biscuits, layer white chocolate again, add dipped biscuits, then refrigerate for 5 minutes.
Return to dark chocolate and repeat the pattern: dark chocolate layer, dipped biscuits, dark chocolate layer, dipped biscuits, refrigerate 5 minutes. Continue alternating between dark and white chocolate sections until the loaf pan is full.
Ensure the final top layer is chocolate. Refrigerate for 5 minutes.
Optional: Spread any remaining white chocolate as a final layer. Place dark chocolate strips down the middle and use a toothpick to drag through to create decorative patterns.
Fill any gaps at the corners of the loaf pan with pieces of cut biscuit.
Refrigerate for at least 1 hour until completely set.
Important: Do not skip dipping the biscuits in the amaretto mixture—this is essential for the structure to hold together and be sliceable. You can substitute rum, espresso, or other liqueurs for the amaretto if desired.