Gras-double is a French culinary term referring to the part of a beef or ox stomach most favoured for cooking.
[1] Although literally translated as 'double-fat' the French term refers to the thickness and color of the lean meat, not its fat content.
According to Larousse Gastronomique, if uncooked it requires 3 to 3½ hours cooking in a salt water court-bouillon.
Pickled gras-double requires 1 to 1½ hours of cooking in salted water.
[1] Larousse lists ten variants of gras-double dishes: Other ways of preparing gras-double include dacquoise (boiled with ham and onions), albigeoise (slow-cooked with vinegar, cloves, garlic and saffron) and languedocienne (cooked, toasted and served with mayonnaise).