Inspired by the vibrant flavors of a traditional niçoise salad, these California-grown russets are baked until fluffy on the inside and crispy on the outside, then loaded with cherry tomatoes, ripe olives, fresh herbs, and a bright and briny vinaigrette.
Use a fork to pierce the skin of each potato several times. Pour 2 tsp of the olive oil over the potatoes and rub to coat evenly. Season with ½ tsp of the salt and roast until tender throughout, 50-60 minutes.
While the potatoes cook, prepare the vinaigrette. In a medium mixing bowl, whisk together the reserved olive brine, minced garlic, dijon mustard, half of the chopped thyme, lemon juice, remaining salt, and black pepper. Continue whisking, slowly drizzling in the olive oil to emulsify the vinaigrette. (Alternately, you can use an immersion blender.) Adjust seasonings to taste and set aside.
In a small bowl, stir half of the chopped capers into the aioli.
Roughly chop the olives and add to a large bowl with the cherry tomatoes and the remaining capers. Drizzle in 4-5 TBSP of the vinaigrette and toss to coat. Gently fold in the tuna and add more vinaigrette to taste.
Once the potatoes have cooled a bit, cut a slit across the top of each and use a small fork to gently fluff the insides. Spread a generous layer of caper aioli across each potato, then top with the olive, tomato, and tuna mixture, and sliced hard-boiled egg. Finish with a generous sprinkle of tarragon, parsley, and the remaining thyme, and a final drizzle of the vinaigrette. Serve immediately.