1. Gently beat the eggs in a bowl until just combined. Avoid overbeating, which creates too many air bubbles.

2. In a separate bowl, combine the dashi stock, soy sauce, mirin (if using), and salt. Stir well.

3. Slowly pour the seasoned dashi stock into the beaten eggs, whisking gently to combine. Maintain the crucial 1:2 egg to liquid ratio.

4. Strain the egg mixture through a fine-mesh sieve into a clean bowl or measuring cup. This removes any unmixed egg white and ensures a smooth custard.

5. Skim off any foam or bubbles from the surface of the strained mixture. This step is vital to prevent pockmarks and achieve a glassy-smooth finish.

6. Divide the mixture evenly into four heatproof chawanmushi cups or ramekins. Add 1 shrimp, 1 slice of kamaboko, and a few shiitake slices to each cup.

7. Place the cups in a steamer basket. Cover the steamer with a lid, preferably wrapped in a cloth to prevent condensation from dripping onto the custard. Steam over a bare simmer (gentle heat) for 15-20 minutes, or until the custard is just set but still slightly wobbly in the center. Do not let the water boil vigorously.

8. Remove from the steamer, garnish with mitsuba or chives, and serve warm.