Preparation:

Step 1:
Begin by toasting the sesame seeds for the dressing. Heat a dry skillet over medium heat and add the sesame seeds. Stir them frequently until golden brown and fragrant, about 2-3 minutes. Once toasted, transfer the seeds to a mortar and pestle or a spice grinder, and grind until the seeds form a rough paste. Set aside.

Step 2:
Next, bring a large pot of water to a boil and add a generous pinch of salt. While waiting for the water to boil, wash the spinach thoroughly. Once the water reaches a rolling boil, blanch the spinach for about 30 seconds, just until the leaves turn bright green and wilt slightly.

Step 3:
Quickly drain the spinach and immediately transfer it to a bowl of ice water to stop the cooking process and preserve its bright green color. After the spinach has cooled, drain it well and squeeze out any excess water. Set the spinach aside.

Step 4:
In a small bowl, prepare the sesame dressing by combining the ground sesame seeds, soy sauce, mirin, sugar, and sesame oil. Mix everything until well combined, forming a thick, aromatic dressing.

Step 5:
Gently toss the blanched spinach with the sesame dressing, ensuring that the spinach is well coated. You can use your hands or a pair of chopsticks to lightly mix everything together.

Step 6:
Transfer the dressed spinach to a serving bowl. Optionally, sprinkle some extra toasted sesame seeds or a small pinch of chili flakes on top for added flavor and presentation.