Bring about 8 cups water to a boil in kettle. Measure 16 cups baby spinach into a large bowl. Pour boiling water overtop to cover. Let stand until spinach wilts, about 1 min. Drain and rinse under cold running water to cool. Squeeze out excess liquid and return to bowl. Stir in 2 tsp each light soy sauce, dark sesame oil and toasted sesame seeds, and 1/2 tsp sugar, and stir to combine.