Crack the eggs into a bowl and whisk gently — avoid bubbles. In another bowl, combine dashi, soy sauce, mirin, and salt. Strain the eggs through a fine sieve and mix into the seasoned broth. This creates a silky-smooth custard base.
Place your fillings (shrimp, fish cake, shiitake mushrooms, chicken) into heatproof ramekins or small cups. Pour in the custard mixture, leaving a little space at the top.
Cover each cup with foil or a lid. Steam over low heat for 12–15 minutes until just set. To test, insert a toothpick: clear broth should rise, not raw egg.
Top with spinach or mitsuba. Serve warm as a side dish or appetizer.