Preheat oven to 350 degrees F.
Slice the onions and cut the cherry tomatoes in half. Mix together in a bowl, then add 1/2 cup sherry vinegar and leave to marinate for 30 minutes.
Place the shallots into a small saucepan and add the remaining 1/2 cup sherry vinegar. Pick off the tarragon leaves, set aside, and add the stalks to the pan. Bring the vinegar mixture to a boil and allow to reduce by 2/3. Remove pan from heat and start to whisk in the diced butter. Keep the pan warm but do not allow it to get hot as this will cause the butter to separate and will split the sauce. When all the butter has been whisked in, pass the sauce through a sieve into a clean pan and keep warm.
Remove the onion and cherry tomatoes from the marinade and place in a saucepan. Sweat the mixture over the medium heat until the tomatoes start to break down. Add approximately 1/2 of the remaining marinade and cook slowly over moderate heat for 30 minutes.
While the tomatoes and onions are cooking, take the sea bass fillets and the scallops and season them with salt and pepper. Sear the sea bass fillets in a very hot non-stick frying pan, skin-side down first. When golden brown, remove from the frying pan, place onto a baking tray and cook in the oven for 3 to 4 minutes. Do exactly the same with the scallops.
Blanch the baby asparagus and chives separately, in boiling, salted water. Remove from the water and tie the asparagus into bundles of 10 using a blanched chive.
To assemble, put 1 piece of sea bass on each plate and top with the confit of tomatoes. Place the second piece of sea bass on top and lean the asparagus bundle against the sea bass. Take the tarragon leaves that were set aside and roughly chop them. Add the tarragon to the warm sauce and spoon sauce around plate. Add a scallop to the side of each plate and serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Stephen Wheeler, Harrods, England