PreparationMake dressing: Whisk together vinegar, mustard, garlic, sugar, 1/2 teaspoon salt, and 1/4teaspoon pepper, then add oil in a slow stream, whisking until emulsified. Make salad: Cook beans in a pot of boiling salted water (2 tablespoons salt for 6 quarts water), uncovered, until tender, 5 to 6 minutes. Immediately transfer with a slotted spoon to a bowl of ice water to stop cooking. Drain beans and pat dry. Add potatoes to boiling water and simmer, uncovered, until tender, about 20 minutes, then drain. Halve potatoes while still warm. Gently flake tuna and toss with 1 tablespoon dressing. Toss potatoes and beans with tomatoes, olives, capers, parsley, and remaining dressing in a large bowl. Season with salt and pepper and top with tuna and eggs.
PreparationMake dressing: Whisk together vinegar, mustard, garlic, sugar, 1/2 teaspoon salt, and 1/4teaspoon pepper, then add oil in a slow stream, whisking until emulsified. Make salad: Cook beans in a pot of boiling salted water (2 tablespoons salt for 6 quarts water), uncovered, until tender, 5 to 6 minutes. Immediately transfer with a slotted spoon to a bowl of ice water to stop cooking. Drain beans and pat dry. Add potatoes to boiling water and simmer, uncovered, until tender, about 20 minutes, then drain. Halve potatoes while still warm. Gently flake tuna and toss with 1 tablespoon dressing. Toss potatoes and beans with tomatoes, olives, capers, parsley, and remaining dressing in a large bowl. Season with salt and pepper and top with tuna and eggs.