Peel of the skin of 300 g Japanese yam (nagaimo) and grate it using a Japanese oroshi grater. Wear gloves if you have sensitive skin.
Transfer it to a mixing bowl and add the whites of 1 egg (save the yolk for later), 1 ½ tbsp Japanese soy sauce (koikuchi shoyu), 1 tbsp Japanese mayonnaise, ½ tbsp mirin and 1 tsp dashi granules.
Mix well until the batter is well combined and slightly bubbly.
Heat your pan on medium-high and grease it with 1 tbsp toasted sesame oil. I recommend a small pan like 20cm/8".
Pour the yam mixture into the pan and fry until air bubbles start to appear on the surface.
Lower the heat to medium and place a lid on top. Steam for 5 minutes (reduce time if you prefer a more runny texture close to Torikizoku's).
Remove the lid and turn off the heat. Top with Japanese mayonnaise, crushed roasted seaweed for sushi (nori) and the reserved egg yolk from earlier.
Give each diner a small plate and enjoy it straight from the pan!