Preheat the oven to 180°C.
Mix rock salt, paprika, and egg whites to create a salt crust.
Cover potatoes in the salt mixture and bake in an ovenproof dish for 40 minutes.
Gently fry diced chorizo in a pan over low heat.
Add 300ml oil and cook slowly for 10 minutes.
Strain the oil through a sieve and reserve both the chorizo meat and the oil.
Whisk egg yolks and vinegar, then slowly drizzle in the chorizo oil to emulsify.
Thinly slice vegetables on a mandolin and soak in ice water.
Combine 300ml oil, Chardonnay vinegar, thyme, and garlic to make a vinaigrette.
Drain vegetables and toss them in the prepared vinaigrette.
Spoon mayonnaise onto plates and arrange dressed vegetables and watercress on top.
Smash the salt crust to release the potatoes and serve immediately.