Bloom the gelatin in cold water.

Sauté diced red onion or shallot in butter until softened.

Add duck livers to the pan and sauté until medium-rare.

Add garlic and nutmeg to the mixture and cook briefly until fragrant.

Stir in Dijon mustard and remove from heat.

Add the bloomed gelatin to the pan.

Transfer the mixture to a blender or food processor.

Drop in the chilled butter, one piece at a time, while blending.

Puree until smooth and creamy.

Season with salt and pepper to taste.

Stir in truffles or herbs/mushrooms, if desired.

Pour the mixture into a mold or ramekins.

Refrigerate for at least 30 minutes to allow the pate to set.