-
1
Place the konbu cold into the donabe or ceramic pot. Pour over the cold water. Set the pot over the lowest possible heat. Do not rush the rise in temperature. The water is ready for the tofu when the konbu begins to swell and small bubbles form at the base of the pot — this is the mineral infusion the dish requires.
-
2
Lower the tofu cubes gently into the konbu water before it reaches a simmer. Maintain the water at 70–75°C throughout — a cook's thermometer is the reliable guide, but visually the surface should show only the faintest shimmer, never a rolling or even a lazy bubble. This is where the dish lives or dies: above 80°C the tofu proteins over-set instantly, producing a granular, tough texture that cannot be corrected; below 65°C the tofu remains cold at the centre and the dish loses all character.
-
3
Hold the pot at 70–75°C for a minimum of 10 minutes before serving. Do not serve immediately after the water reaches temperature. The tofu is ready when a cube, lifted on a wide spoon, feels uniformly warm through to its centre when touched lightly — it will have a faint translucency at the outer surface and hold its shape without resistance.
-
4
While the tofu warms, prepare the Okutan dipping sauce: combine the dashi, soy sauce, and mirin in a small saucepan and warm gently — serve warm, not cold. Arrange the yakumi in small individual dishes at the table.
-
5
Serve directly from the pot at the table, ladling tofu and a little konbu water into individual bowls immediately before eating. Each diner seasons with warm dipping sauce or ponzu and adds yakumi to taste. The tofu is spent when its delicate sweetness has gone; the remaining konbu water may receive shirataki noodles as a natural shime to close the meal.