Drop the potatoes into well-salted boiling water and cook until a knife slides through easily, about 12-15 minutes depending on size. They should be tender but not falling apart — you want them to hold their shape when quartered.
⏱ 15 min
Lower eggs into boiling water and cook for exactly 10 minutes for jammy yolks that still have a touch of creaminess. Transfer immediately to an ice bath to stop the cooking, then peel once cool and halve lengthwise.
⏱ 10 min
Blanch the green beans in rapidly boiling salted water for 3 minutes — they should be bright green and still have some snap. Shock them in ice water to preserve that vibrant color and crisp-tender texture.
⏱ 3 min
Whisk together the vinegar, mustard, salt, and pepper until smooth, then slowly stream in the olive oil while whisking constantly. The mustard helps everything emulsify into a creamy, cohesive dressing.
Quarter the warm potatoes and gently toss with 2 tablespoons of the vinaigrette. The potatoes will absorb the dressing better while they're still warm, creating more flavorful bites throughout.
Spread the greens across a large platter, then arrange each component in distinct sections — this is a composed salad, so keep the tuna, eggs, tomatoes, beans, potatoes, and olives separate and visually appealing. Add the onion slices if using.
Drizzle the remaining vinaigrette over everything, letting people see each beautiful component. Lay the anchovy fillets on top if you're using them — their briny punch is traditional and worth it.