Start by filling a small pot with 1 liter water and adding 5 g dried kelp (kombu). Soak for 30 minutes to create a light kombu dashi.
While you wait, cut 350 g silken tofu into 6-8 large cubes.
Mix the sauce ingredients (1 ½ tbsp sesame paste (nerigoma), 1 tbsp Japanese soy sauce (koikuchi shoyu), 2 tbsp water, 1 tsp chili oil (rayu), 1 tsp rice vinegar and ½ tsp sugar) to a small food processor and blitz until combined. (Alternatively, mix thoroughly by hand.)
Once the kombu has rehydrated, place the pot on the stove and heat over medium until almost boiling. Reduce the heat to low, remove the kombu (discard or repurpose to make kombu tsukudani) then add the tofu and sprinkle ¼ tsp salt into the broth.
Simmer until the tofu is warmed through.
Use a slotted spoon to transfer the tofu pieces to serving bowls. Drizzle with the sesame sauce and sprinkle with finely chopped green onions. Enjoy!