4 large eggs
For the Broth (optional; see note about substituting instant dashi):
2 tablespoons (30ml) mirin
2 teaspoons (8g) sugar
1/2 cup (120ml) soy sauce
3/4 cup (180ml) homemade or instant dashi
Thinly sliced scallions, for garnish
For the Eggs, If Using an Immersion Circulator: Following manufacturer’s instructions, preheat water bath to 75°C. When water is ready, add shell-on eggs and cook for 13 minutes. Transfer to an ice bath to chill. Eggs can be refrigerated, shell on, for up to 2 days.
For the Eggs, If Using a Pot and an Instant-Read Digital Thermometer: Fill a large pot with water and bring to 75°C. Add shell-on eggs and cook for 13 minutes, adjusting heat as necessary to maintain temperature. Alternatively, transfer hot water to a cooler, add eggs, and cook for 13 minutes, using extra boiling or cold water to adjust heat to maintain 167°F. A small fluctuation of a degree or two up or down is okay; just do your best to maintain the temperature the entire time. Transfer eggs to an ice bath to chill. Eggs can be refrigerated, shell on, for up to 2 days.
For the Soy-Dashi Broth (optional): While eggs cook, bring mirin to a simmer over medium heat in a small saucepan. Add sugar and stir to dissolve. Add soy sauce, stir well, and bring to a simmer. Remove this soy-mirin mixture from heat and transfer to the refrigerator to cool.
When ready to serve, combine 1/4 cup soy-mirin mixture with 3/4 cup dashi. Any additional soy-mirin and dashi can be reserved for another use. (Mixed together, as in this recipe, they make an excellent cold dipping broth for chilled soba or udon noodles.)
Working with one at a time, carefully crack eggs and peel off enough of the shell to slide the egg out into a small mixing bowl. Using a spoon and/or a clean paper towel, a carefully separate soft-cooked egg from any loose whites. Slide each egg into a small serving bowl, pour broth around it, and garnish with scallions. Serve.