Place buckwheat into TM bowl and mill 5 sec/speed 6.
Add remaining base ingredients and blend 30 sec/speed 8.
Press into a square tin with removable base and refrigerate.
Place all ingredients into TM bowl and mill 40 sec/speed 8. Press on top of cold base and return to the refrigerator.
Place all ingredients into TM bowl and melt 6 min/60°C/speed 1, stopping to scrape down sides of bowl as needed.
Pour on top of filling and spread quickly with a palette knife. The ganache will set quickly on a cold surface, so you will need to work fast to get an even finish. Tap the tin on the bench to level the surface and return to the fridge.
To cut into squares, use a wet knife and wipe between each cut.