First make the mash, chop the potatoes and place in a pot and cover with cold salted water and bring to a boil. Reduce the heat and simmer for about 15-20 minutes, until the potatoes are tender, then strain and mash them thoroughly. Beat in the butter and cream and season well and stir in the basil.
Next make the dressing by whisking the olive oil with the lemon juice until it emulsifies. Then remove the skins from the tomatoes by placing the tomatoes in a bowl of boiling water, leave for 15 seconds and remove the loosened skin. Cut the tomatoes into quarters and remove the seeds and cut the skin into small dice and add to the dressing along with the shredded basil and season to taste.
Trim the asparagus and peel the base to remove the tough skin. Place in a dish and drizzle with the olive oil and balsamic and leave to marinate for about 10 minutes. Remove from the marinade and sear on a hot pan.
Season the sea bass with a little salt and pepper and heat a frying pan with the olive oil. Fry the fillets in the pan for about 1-2 minutes on each side until golden.
To serve, place some basil mash in the centre of a dish and lay the fish on top, with some asparagus. Drizzle with the basil dressing.