Ingredients
6 ounces red potatoes, scrubbed and cut into 1/2-inch chunks
3 ounces thin green beans, trimmed
1 large egg
2 tablespoons Dijon mustard
2 tablespoons red wine vinegar
1/3 cup extra-virgin olive oil
1/2 ounce Nicoise olives (about 12 olives), pitted and coarsely chopped
1 medium shallot, cut into 1/4-inch dice (about 1/4 cup)
1 can (6 ounces) best-quality water-packed solid white tuna, drained
1 tablespoon finely chopped fresh flat-leaf parsley
1/4 teaspoon coarse salt
Freshly ground pepper
6 pieces baguette (6 inches long and 2 ounces each), split lengthwise
3 small tomatoes, thinly sliced
Preparation
Cover potatoes with 2 inches of cold water in a medium saucepan. Bring to a boil. Reduce heat to medium-low; simmer until potatoes are tender, about 5 minutes. Drain potatoes, and let cool completely; set aside.
Prepare an ice-water bath; set aside. Fill saucepan with cold water, and bring to a boil. Add green beans; cook until bright green, about 1 minute. Using a slotted spoon, transfer green beans to ice-water bath to stop the cooking; let cool completely. Cut green beans into 1/2-inch pieces; set aside.
Refill ice-water bath; set aside. Fill a small saucepan with cold water; add egg. Bring to a boil. Remove from heat; cover, and let stand 11 to 12 minutes. Transfer egg to ice-water bath; let stand 2 minutes. Peel egg, and cut in half; discard yolk. Cut egg white into 1/2-inch pieces, and set aside.
Whisk together mustard and vinegar in a small bowl. Whisk in oil in a slow, steady stream; set vinaigrette aside. Put potatoes, green beans, egg, olives, shallot, and tuna into a large bowl. Sprinkle with parsley and salt; season with pepper. Drizzle vinaigrette over tuna mixture; gently stir to combine.
Using your hands, hollow out 1 half of each baguette piece, leaving a thin layer of bread. Arrange tomato slices over remaining half. Spoon 1/2 cup tuna salad onto hollowed-out half, and top with tomato-lined half.
