Cut 2 chicken tenders into small pieces and toss with 1 tablespoon of sake.
Gently whisk 3 large eggs with 1¾ cups of dashi, 1 teaspoon of mirin, 1 teaspoon of usukuchi soy sauce, and ½ teaspoon of kosher salt. Strain through a fine-mesh sieve.
Divide the chicken, 8 thin slices of kamaboko, and 50g of shimeji mushrooms between heatproof cups of about 200ml. Pour in the egg mixture until each cup is about 80% full.
Steam the cups over the lowest heat, lid slightly ajar, for about 20 minutes, until set; keep the water at 176-194°F / 80-90°C so it never boils. Top with 4 sprigs of mitsuba.
