Preheat the oven to 180C/350F/Gas 4.
For the salt baked potatoes, mix the salt, paprika and egg whites together. Cover the bottom of an ovenproof dish with the mixture and place the potatoes in the dish. Completely cover with the remaining salt mixture and bake for 40 minutes.
For the chorizo mayonnaise, gently fry the chorizo over a low heat in a deep pan (don’t colour too much). Add the oil and cook slowly for 5-10 minutes.
Leave to cool for 10 minutes, then pass through a fine sieve to separate the meat and oil, retain both.
Whisk together the egg yolks and white wine vinegar. Slowly add the reserved oil in a thin stream, whisking all the time, until the mixture has emulsified and resembles mayonnaise. Set aside.
For the escabeche of vegetables, thinly slice all the vegetables on a mandolin and place in a large bowl of ice-cold water.
Mix the Chardonnay vinegar and oil to make vinaigrette. Add the thyme and garlic. Drain the vegetables and add to the vinaigrette.
To serve, spoon out the mayonnaise and swirl into a circle in the centre of each plate. Dress the plate with the vegetables and garnish with watercress. Sprinkle with the reserved chorizo and season with black pepper.
Turn out the salt baked potatoes and smash the salt to release the potatoes. Serve alongside the mayonnaise and vegetables.