Boil the potatoes for 8 to 10 minutes until tender.
Drain potatoes, toss with 2 tablespoons of olive oil, and season with salt and pepper.
Season sea bass fillets with black pepper.
Heat a frying pan with 2 tablespoons of olive oil and fry fish for 2 to 3 minutes per side.
Remove fish from the pan and let rest for two minutes.
Blanch watercress in boiling salted water for 1 minute then refresh in iced water.
Purée watercress with salsa verde ingredients in a food processor and season to taste.
Serve potatoes and sea bass on plates topped with a spoonful of salsa verde.