Place the sesame seeds over a medium heat pan and cook until they just start to brown. Reserve 1 tablespoon of the sesame seeds and place the remainder in a small blender or grinder. Once a rough paste forms, add the mirin, soy, miso and honey.
Bring a large pot of boiling water to the boil. Add the spinach stalks first as they will take the longest to cook and then submerge the leaves. Cook for 1-2 minutes and then plunge into a bowl of iced cold water. Squeeze out excess water and place in a clean tea towel to squeeze even more of the liquid.
Roughly chop spinach and place in a shallow platter, drizzle over sauce and sprinkle on the extra toasted sesame seeds.