In a small bowl, combine the shallot, vinegar, lemon juice, and mustard. Let sit 10 minutes. Whisk in the oil. Season with salt and pepper.

Bring a large pot of water to a boil. Add the potatoes and cook until tender, about 8 minutes. Drain and pat dry.

Add the pancetta to a large skillet set over medium heat. Cook until browned and crisp, about 3 minutes. Using a slotted spoon, transfer the pancetta to a paper towel to drain.

Add the potatoes to the skillet, cut-side down. Cook 5-8 minutes, or until crisp and golden brown. Stir in the pancetta and peas and cook 1 minute, or until heated through. Remove from heat and add the dressing. Stir in the radishes, celery leaves, and capers. Sprinkle with chives. Serve immediately.