Trim the spinach roots and make cross cuts at the base. Wash thoroughly in a bowl of water, shaking to remove dirt. Drain and set aside.

Boil water in a pot and add salt. Cook spinach in batches, starting with the roots for 30 seconds, then the leaves for 10 seconds. Drain and cool. Squeeze out excess water and cut into 5cm pieces. Mince the ginger.

Heat salad oil in a clean pot over medium heat. Add ground chicken and minced ginger, cooking until the chicken changes color.

Add the seasoning ingredients (sake, mirin, soy sauce, dashi powder, and water) and bring to a boil. Cover and simmer on low heat for 5 minutes. Add the potato starch mixture and stir to thicken.