Thon à la Marseillaise

The first lettuce reportedly arrived in France from Italy with the Avignon popes in the fourteenth century, hence the name romaine, or Roman, lettuce. Firm lettuce of this type is excellent cooked, losing its crispness but gaining an acidity that nicely balances the richness of tuna. You do not need expensive sushi-grade tuna for this recipe; other robust fish, such as swordfish and halibut, will do. On a hot day, this dish is good served at room temperature, so it can be cooked an hour or