Start by hard-boiling the eggs—place them in a pot of cold water, bring to a boil, then remove from heat and let sit covered for 10 minutes before transferring to ice water. While the eggs cool, trim the green beans and begin boiling a pot of salted water for the potatoes. I always use small waxy potatoes for Niçoise because they hold their shape beautifully when cut. Once the water boils, add the potatoes and simmer until just tender, about 15-20 minutes depending on size. In the final minutes of potato cooking, blanch the green beans in the same pot or a separate pot of boiling water for 2-3 minutes until bright green and tender-crisp, then immediately shock them in ice water to stop the cooking and preserve their color and texture.

While the potatoes and eggs cook, prepare the dressing by combining the minced garlic clove with the salt in a small bowl or jar—this helps break down the garlic into a fine paste and prevents harsh raw garlic flavor. Add the Dijon mustard and whisk together, then add the lemon juice and let sit for a minute to allow the flavors to meld. Finally, add the olive oil and shake or whisk vigorously for 30 seconds until emulsified and creamy. I prefer using a jar with a tight-fitting lid so I can shake rather than whisk—it's faster and creates a better emulsion. Taste and adjust seasoning with additional salt and pepper as needed.

Tear or roughly chop the cos lettuce and arrange it as a base on individual plates or a large serving platter. Drain the cooled potatoes and cut into 1-inch cubes, then arrange them in neat sections around the plate. Drain the green beans thoroughly and pat dry with paper towels, then arrange in another section. Quarter the Roma tomatoes and place in their own section. Slice the hard-boiled eggs from Step 1 into quarters and position them on the plate. Add the drained tuna in large chunks rather than breaking it up too much—this keeps the salad more elegant and textured. Scatter the olives and capers across the salad, then finish with fresh parsley.

Drizzle the vinaigrette from Step 2 generously over the assembled salad, or serve it on the side for guests to dress their own portions. Toss gently if desired, though the traditional presentation keeps components separate and distinct on the plate.