How to Make It
Sprinkle fillets with 1/2 teaspoon salt. Combine wine, orange zest and juice, and garlic in a 10-inch pot. Place celery in a single layer in the pot, making a “raft” for the fish. Bring to a boil over medium-high. Place fillets on celery raft; reduce heat to medium to maintain a simmer. Cover; steam fillets until cooked through, about 7 minutes. Transfer fish to a plate.
Combine steaming liquid, 2 cooked garlic cloves (discard remaining garlic), watercress, cooked celery, and olive oil in a blender, and puree until smooth. Add sugar, coriander, and remaining 1/2 teaspoon salt. Divide sauce among 4 shallow bowls. Top with fish, orange sections, and watercress.