Let the foie gras sit at room temperature for 30 minutes and remove the veins and unwanted parts.
Sprinkle the pieces with salt and pepper, making sure to coat them well.
Place the foie gras in an airtight container and let it rest in the refrigerator for 24 hours.
After 24 hours, take the foie gras out of the refrigerator, add the cognac and let it return to room temperature for about 1 hour.
Preheat the oven to 100°C.
Fill a terrine with the marinated foie gras, cover it and place it in a high-sided dish. Pour warm water up to one-third of the terrine. Bake in a bain-marie for about 30 minutes. Remove the terrine from the oven. Place another terrine on top to press it well and bring the fat to the surface.
Set aside the foie gras in the refrigerator for 24 hours with the press. Remove it and place the foie gras back in the fridge for 3 days before tasting.
