Ingredients
1 pound russet potatoes (about 2 whole large potatoes), peeled and cut into large chunks
Salt
2 eggs
1 tablespoon rice vinegar, plus more to taste
2 teaspoons sugar
1 small Japanese or Persian cucumber, or 1/2 an English cucumber (about 4 ounces), quartered lengthwise, seeds removed and discarded, and thinly sliced
1 small carrot (2 to 3 ounces), quartered lengthwise and thinly sliced
1/2 cup thawed frozen corn kernels or briefly boiled fresh corn kernels (optional)
1/4 cup chopped radish (about 2 radishes; optional)
2 scallions, thinly sliced
5 tablespoons Kewpie mayonnaise (see Tip), plus more to taste
1 whole sac mentaiko or tarako (about 2 ounces)
1 teaspoon grated lemon zest
1 teaspoon fresh lemon juice, plus more to taste
Freshly ground black pepper
Directions
1
In a medium saucepan, cover the potatoes with cold water by at least 1 inch. Add a few big pinches of salt. Bring to a boil over high heat. Gently lower the eggs into the pot. Cover, reduce to a bare simmer, and cook until the potatoes are tender and show no resistance when pierced with a knife or cake tester, 10 to 12 minutes. Drain the potatoes in a colander and spread in a single layer on a large rimmed baking sheet. Immediately sprinkle with vinegar and sugar. Set aside until completely cool, at least 15 minutes. Transfer the eggs to a bowl of ice water and peel when completely cool.
2
Meanwhile, toss the cucumber with a big pinch of salt in the bottom of a large bowl and set aside until the potatoes are cool.
3
When the potatoes are cool, add them to the bowl with the cucumber and lightly mash with the back of a fork until some bite-size chunks still remain.
4
Add carrot, corn, radish, scallion, mayonnaise, mentaiko, lemon zest and juice. Squeeze the hard-boiled eggs through your clean fingers to break them up, or chop them with a knife and add them to the salad. Stir together and season with pepper, more salt, sugar, vinegar, lemon juice or mayonnaise, or a combination, to taste.
Notes
Kewpie is a Japanese brand of mayonnaise with a thicker texture, and tangier, more umami flavor, though any mayonnaise you prefer will work in this recipe.