Clean the duck livers and soak them in heavy cream overnight. Remove the liver from the cream and blot dry. Season with salt and pepper.
In a sautè pan, heat up the oil until just about smoking. Sear both sides of the liver unil medium rare.
When the liver are all seared and removed from the same pan, add the onions to the pan and sautè the onions.
Deglaze the pan with chardonnay and reduce until the wine is a glaze.
Add the heavy cream and mirin. Reduce the cream down to half nand season with salt and pepper.
Blend the liver and cream mixture in the blender until smooth.
Add the butter cubes slowly until emulsified.
Strain the liver through a chinois and adjust seasoning.
chill or use right away.