Blanch the potatoes in boiling water, drain, and slice them in half.
Boil the green asparagus, broad beans, peas, soy beans, and spring onions for two minutes.
Drain the vegetables and rinse under cold water briefly to stop the cooking process.
Place the blanched vegetables on a tray with potatoes, drizzle with olive oil, and season.
Macerate the purple asparagus in a bowl with lemon juice and salt to soften.
Whisk mustard and vinegar together, then slowly add oils until a thick sauce forms.
Combine all vegetables, shallots, herbs, and greens in a bowl and coat with the dressing.
Divide the salad among four plates and serve immediately.