This is a staple recipe in my house. My pantry is always stocked with the basics like soy and mirin. If you don't have sake on hand, feel free to sub it out for sherry or white wine. Teri means "glaze" or "sauce" and yaki means "grill." Traditionally a piece of fish would be grilled over hardwood charcoal and then glazed with a luscious sauce that's sweet, salty and very savory. This version would be a Japanese home-cook version where all the work is done in one pan. I'm a believer that you can make better sauces than store bought. This teriyaki sauce recipe can be multiplied, shaken together in a bottle and held in the fridge until ready to use.
For the teriyaki sauce: Mix all the ingredients in a small saucepan and bring to a simmer over medium heat; whisk about 1 to 2 minutes until the sugar dissolves and the sauce bubbles and thickens slightly. Set it aside to use on the salmon and store any leftovers in the refrigerator.
For the fish: Pat the fish dry with a paper towel, cut into four 3-inch pieces, and season it with salt and pepper. Heat the vegetable oil in a large heavy-bottomed skillet over medium-high heat. Once you start to see white smoke, lay the fish flesh-side down in the skillet. Move the fish around constantly while cooking to keep it from sticking. When the fish is medium, 4 to 6 minutes, turn with a spatula only once.
Cook the other side for another minute. Add the teriyaki sauce to the pan and reduce the heat to low. The sauce will begin to simmer and reduce. Tilt the pan around a few times and turn the fish until it's well coated with the sauce.
To serve, cut the baby bok choy into quarters and arrange on a platter. Place the salmon over top and drizzle with the sauce from the pan. Sprinkle the toasted sesame seeds and scallions over the salmon. Serve with rice on the side.