Scallops are easy to prepare, but care must be taken not to overcook them. They're best lightly seared, so they're still basically raw inside, although some people like them a little more cooked than that. For this dish, buy fresh shell-on scallops, with the roe attached. Be sure to save the prettier shells for serving.
This beurre blanc ("white butter") sauce uses French beurre aux algues (seaweed butter), which is sold at specialist shops. If you can't find it, make the beurre blanc with 125g salted butter and, just before you take the sauce from the heat, add a good pinch of shredded nori (Japanese dried seaweed).
If you can't find shichimi togarashi (Japanese seven spice powder), use toasted sesame seeds and a small amount of chilli flakes.
Bring a pot of salted water to the boil, and add the edamame. Frozen pods need only about 30 seconds to reheat; fresh edamame takes about eight minutes to cook. Whichever you use, when they're ready, drain them in a colander and rinse with cold water. Remove the pods, then pull off the skin that surrounds each soybean. Place the prepared soybeans on a clean dish towel to dry while preparing the other ingredients.
Make the beurre blanc. Finely mince the shallot. Heat the oil in a small pan, add the shallot and cook it over a low flame until soft, stirring often. Turn the flame to medium, then add the sake. Simmer it until it reduces to about two teaspoons. Add the cream and simmer until the liquid is reduced to about one tablespoon. Turn the heat to low and, whisking constantly, add the seaweed butter one or two cubes at a time. Let the butter incorporate almost fully before adding more. After whisking in all the seaweed butter, add the unsalted butter, again, just one or two cubes at a time. If you add the butter too quickly, the emulsion might curdle. The beurre blanc will be thick but spoonable. Taste for seasoning and add salt, if necessary. Place the pan over a small bowl of hot (but not boiling) water, to keep it warm while cooking the scallops.
Use paper towels to dry each scallop thoroughly (if it's moist, it won't brown well in the skillet). Put the butter and oil in a large skillet and place it over a medium-high flame. When the butter melts and sizzles, swirl the pan to combine the fats. Lightly salt the scallops and place immediately in the skillet. Let the scallops cook undisturbed for about two minutes - they should be well browned on one side (if necessary, increase the heat). Flip them over and cook the other side for another minute or two, depending on how well you like them cooked.
Place the scallops in the reserved scallop shells and spoon some of the beurre blanc over each one. Top each scallop with some shredded nori, then sprinkle with a little black pepper and shichimi togarashi. Scatter some soybeans on each plate and serve immediately.