Step 1Start making the green onion puree about 30 minutes before cooking the fish. Cut the green onions in half crosswise, separating the white part from the green. Place the white halves in a medium saucepan with 3 tablespoons butter and 2 tablespoons water. Simmer very slowly until tender, about 10 minutes. Add half of the green portions (reserving the remaining green portions for garnish) and cook for one minute.
Step 2Remove from the heat and puree in a blender or food processor. Pass the puree through a coarse strainer into a clean saucepan, pressing on the onions with the back of a rubber spatula. Discard the onion solids remaining in the strainer.
Step 3Rewarm gently as the fish is cooking, adding a little water to thin the sauce consistency, if necessary. Just before serving, stir in the remaining butter. Season with the vinegar and salt and pepper to taste. Makes one-half cup sauce.
Step 1Score the skin of each fish fillet, making lines about three-fourths of an inch apart and cutting into the flesh as little as possible. Carefully dip the skin side of each fillet first into the milk, then into the seasoned flour. Repeat. Continue with remaining fillets. Do not get any flour on the flesh side of fish.
Step 2Pour peanut oil to a depth of one-fourth of an inch into large saute pan (or 2 saute pans) and heat over medium heat. Lay fillets in, skin side down. Cover the pan loosely with a lid or pie tin. The fish should be sizzling. (While skin is crisping, flesh is steaming.) Cook 5 to 7 minutes, until a very sharp knife inserted into the thickest part of fillet pierces easily.
Step 3Spread the green onion puree over four plates and lay each fillet, skin side up, on top of the puree. Thinly slice the reserved green onions on the diagonal; sprinkle over the fish.