Prepare the foie gras: Trim away veins and connective tissue. Slice into small chunks and keep chilled.
Cook foie gras: Lightly sear or poach until soft but not fully melted. Remove from heat and let cool slightly.
Blend mousse: In a food processor or blender, combine foie gras, cream, butter, salt, and pepper. Blend until smooth and airy. Add cognac or optional flavorings gradually.
Strain mixture: Push mousse through a fine mesh strainer or chinois for an ultra-smooth texture.
Set mousse: Transfer mousse to ramekins or molds and smooth the surface. Refrigerate for 4–6 hours or overnight to firm up.
Serve: Allow to sit at room temperature for 15–20 minutes before serving. Serve with toasted brioche, crackers, or fruit preserves.
