Allow the foie gras to come to room temperature for 1 hour.
Make a shallow incision in the centre of the foie gras and open it gently. Devein it (gently remove the blood vessels) using tweezers or the tip of a knife. Place the foie gras in a glass dish. Sprinkle with the salt and sugar on both sides. Season with pepper. Drizzle with the Armagnac. Cover with plastic wrap and refrigerate for 1 hour or up to 24 hours.
Pat the foie gras dry and place it in the jars, pressing well. Close the jars and place them in a saucepan. Add enough hot water to fill the saucepan three quarters up the jars. Cook in barely simmering water for 15 to 20 minutes or until a thermometer inserted into the centre of the foie gras reads between 45 and 50 C (113/122 °F).
Remove the jars from the water and let cool for about 30 minutes. Refrigerate for at least 24 hours.
Will keep in the refrigerator for about 15 days. Consume within 24 hours after opening the jars.
Marinating the foie gras allows the remaining blood vessels to drain their blood. Some even submerge the liver in milk to properly disgorge the liver to achieve a nice uniform color.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.