8large eggsLarge size, and room temperature is crucial!
water for boiling
Marinade
1cupprepared warm dashi (or just warm water)Instant is ok.
3tbspsugar
8tbsplight soy sauce
4tbspmirin
4tbspsake
Equipment
1timer
1gallon sized sealable plastic bags
1large bag clip
Instructions
Pull your eggs out of the fridge for 1-3 hours to get them to room temperature.
Prepare an ice bath in a large mixing bowl with about 2 cups of ice and 2-3 cups of water.
Get enough water boiling in a pot on high heat so that after you add the eggs there's at least one inch of water above the eggs. Once it hits a boil lower the temperature slightly so it maintains a low boil.
Gently lower the eggs into the boiling water one at a time so they don't crack. You can do this quickly with a large ladle so timing on all the eggs are even. Start your timer immediately for exactly 6 minutes 30 seconds.
When the timer's up, take out all the eggs as quickly as possible and transfer to the ice bath. Ladle the ice water over the eggs, and gently stir to evenly chill, for exactly 2 minutes. Remove the eggs from the bath, gently remove the shells, and set aside.
In a mixing bowl, make the dashi according to the packet instructions, so that you have 1 cup of prepared dashi. This should be done with warm water. If you're substituting dashi for just water, also make sure it's warm.
Add the sugar first, and stir so it dissolves, then add the rest of the marinade ingredients and stir to combine.
Pour the marinade into the bag, and add the eggs. The clip will help the marinade completely cover the eggs. If you don't have a bag or clip you can marinade in a bowl or tray, but it will take more liquid to completely cover the eggs. You can also use that method and just rotate the eggs every half day or so, but the results will be slightly different.
Transfer to the refrigerator for at least two days. Eat within 2-3 days as the optimum window, but remove from the marinade after 3 days if you can't use them all right away.
Notes
The weird thing about the dashi is that you can barely taste the difference. It did make a difference with a lighter more even color on the eggs though. If you can't find dashi, feel free to skip it.
Egg size is crucial to the timing! If you must use larger eggs, boiling time may be longer, and for smaller eggs boiling time may be shorter. This will affect the ice bath time too.
Getting the eggs to room temperature first also helps us precisely get the egg timing down. I found that if you do it straight out of the fridge, it was harder to get the center of the yolks cooked without overcooking the outer edges of the yolk.