1. Heat oven to 200 degrees F. Heat a large, heavy skillet over medium heat. Place sesame seeds on a plate and season with salt and pepper. Add the oil to the skillet. When it shimmers, begin to turn the fillets in the seeds, coating the fillets as fully as possible. Add the fillets to the skillet.
2. Brown the fish on one side for a couple of minutes, then turn and brown on the other side, another minute or two. Remove the skillet from the heat and transfer the fish to a plate (don't worry if its done); put the plate of fish in the oven to keep warm.
3. When the skillet has cooled slightly, return it to the stove over medium heat. Add the butter and, when it melts, the ginger. About 30 seconds later, add the soy sauce and 1/4 cup water and stir to blend. Return the fillets to the skillet, along with any of their accumulated juices.
4. Turn heat to medium and cook the fillets for a total of about 4 minutes. (If at any point the pan seems to dry out, add 2 or 3 tablespoons water.) At this point, the fish should be done (a thin-bladed knife inserted into its thickest point will meet little resistance). Serve with the pan juices spooned over the fish. Makes 4 servings.