Mince or finely slice the shallot with a mandoline. Transfer shallots to a large bowl and cover with the sherry vinegar. Add some salt and pepper and stir. Make sure that the shallots are covered in vinegar. Set aside to soften for at least 5 minutes.
Place the potatoes in a medium saucepan and cover them with water. Place the saucepan on medium-high heat and bring the potatoes to a boil. Lower the heat to a simmer and cook potatoes until they are just tender, about 13-16 minutes. Using a slotted spoon, transfer cooked potatoes to a plate or bowl and allow them to cool slightly. Reserve the cooking water.
To the bowl with the shallots, stir in the capers and mustard. While whisking, slowly drizzle the olive oil into the bowl. Whisk until you have a unified dressing. Once you can handle the potatoes, cut them into quarters and place them in the bowl with the shallot dressing. Add the white beans and celery to the bowl as well. Stir to combine and set aside.
Bring the saucepan of water back up to a boil and add a pinch of salt. Cut the asparagus and green beans into bite-sized pieces and add them to the saucepan. Boil vegetables until tender, about 3-4 minutes. Drain the vegetables and place them in an ice bath or run them under cold water to shock them and stop the cooking process.
Dry the asparagus and green beans with a kitchen towel and add them to the bowl with the potatoes, white beans etc. Add the radishes, chives, and parsley as well, and toss everything to combine. Check the salad for seasoning and add more salt and pepper if necessary. Serve immediately or store in a sealed container in the refrigerator for up to 3 days.