Japanese Potato Salad with Kewpie Mayo and Ham

Why You’ll Love This Recipe

• Classic Japanese deli flavor: creamy, gently sweet, and just tangy enough.
• Softly mashed potatoes with crisp, juicy cucumber for the perfect texture contrast.
• Make-ahead friendly—great for bento boxes, cookouts, or weeknight dinners.
• Uses easy-to-find ingredients with simple, reliable steps.

Grocery List

• Produce: Yukon Gold potatoes, Japanese (or English) cucumber, carrot, small onion, optional chives
• Dairy: Milk
• Pantry: Kewpie mayonnaise, rice vinegar, sugar, kosher salt, black pepper, optional Japanese mustard (karashi) or Dijon

Full Ingredients

Main Salad

• 2 lb (900 g) Yukon Gold potatoes, peeled and cut into 1-inch chunks
• 1 medium Japanese cucumber (150 g), thinly sliced into half-moons
• 1/2 tsp kosher salt (for salting the cucumber)
• 1 small carrot (80 g), cut into 1/8-inch (3 mm) dice
• 1/4 small onion (40 g), very thinly sliced
• 4 oz (115 g) deli ham, cut into thin ribbons or 1/2-inch pieces

Seasoning for Hot Potatoes

• 1 tbsp (15 ml) rice vinegar
• 1 1/2 tsp (6 g) sugar
• 1/2 tsp kosher salt

Dressing

• 1/2 cup (120 g) Kewpie mayonnaise
• 2 tbsp (30 ml) milk
• 1 tsp (5 g) Japanese mustard (karashi) or Dijon (optional, for a subtle kick)
• 1/2 tsp freshly cracked black pepper, plus more to finish

For the Pot

• 1 tbsp kosher salt for the cooking water
• Cold water to cover potatoes by 1 inch (about 2 qt/2 L)

Step-by-Step Instructions

Step 1: Salt the cucumber and mellow the onion

Place the sliced cucumber in a bowl and sprinkle with 1/2 tsp kosher salt. Toss and let stand for 10 minutes to draw out excess water. Meanwhile, place the sliced onion in a small bowl of ice water for 5 minutes to take off the sharp bite, then drain well and pat dry.

Step 2: Cook the potatoes (and blanch the carrots)

Put the potato chunks in a medium pot and cover with cold water by 1 inch. Add 1 tbsp kosher salt. Bring to a boil, then lower to a brisk simmer at 195–205°F (90–96°C). Cook until a skewer slides through with little resistance, 12–15 minutes. During the last 2 minutes of cooking, stir in the diced carrots to blanch. Drain thoroughly.

Step 3: Steam-dry and season the potatoes

Return the drained potatoes to the warm pot over low heat and shake for 30–60 seconds to evaporate surface moisture. Remove from heat. Sprinkle evenly with 1 tbsp rice vinegar, 1 1/2 tsp sugar, and 1/2 tsp kosher salt. Toss gently to coat while hot—this seasons the potatoes all the way through.

Step 4: Roughly mash and cool slightly

Using a masher or fork, mash the potatoes just until creamy with some small chunks left for texture (aim for about 70% smooth, 30% chunks). Spread the potatoes in a shallow bowl so they cool to warm—not hot—about 10 minutes (roughly 100°F/38°C). While the potatoes cool, squeeze the salted cucumber firmly in handfuls to remove excess liquid.

Step 5: Whisk the dressing

In a large mixing bowl, whisk together Kewpie mayonnaise, milk, and mustard (if using) until smooth and glossy. Add the cracked black pepper.

Step 6: Fold everything together

Scrape the warm potatoes into the bowl with the dressing and fold gently to coat. Add the squeezed cucumber, drained onion, blanched carrot, and ham. Fold just until combined so the potatoes stay fluffy. Taste and adjust: add a pinch of salt, an extra 1–2 tsp rice vinegar for tang, or more pepper as desired.

Step 7: Chill and serve

Cover and chill for at least 30 minutes and up to 24 hours so the flavors meld and the salad firms slightly. Serve with an extra shower of freshly cracked black pepper. If you like, garnish with snipped chives.

Pro Tips

• Season potatoes while hot with vinegar and sugar—this locks in tang and gentle sweetness before the mayo goes on.
• Salt and squeeze the cucumbers to keep the salad from becoming watery.
• Mix the salad while the potatoes are warm (not hot) so the mayo doesn’t separate and the dressing clings beautifully.
• Leave some potato chunks for that signature Japanese deli texture.
• Hold back 1–2 tbsp mayo to stir in just before serving if making ahead—it refreshes the creaminess.

Variations

• Egg Lover’s: Fold in 2 hard-boiled eggs, roughly chopped, for extra richness and protein.
• Fruity Crunch: Add 1/2 small crisp apple (Fuji), cut into fine matchsticks, for a classic sweet note found in many Japanese homes.
• Vegetarian: Skip the ham and add 1/2 cup (75 g) thawed edamame or 1/2 cup sweet corn kernels.

Storage & Make-Ahead

Refrigerate in an airtight container for up to 3 days. Do not freeze. For best texture, fold in most of the mayo on day 1 and hold back 1–2 tablespoons to stir in just before serving. Great make-ahead side for picnics and bento—keep chilled (below 40°F/4°C) and avoid leaving out more than 2 hours.

Nutrition (per serving)

Approximate per serving (1/6 of recipe): 290–310 calories; 17 g fat; 30 g carbohydrates; 6 g protein; 2 g fiber; 480 mg sodium. Values will vary with ham and mayo brands.