Dashi and soy sauce add umami to buttery leftover mashed potatoes in this cozy soup from chef Shota Nakajima. As a kid, whenever he was hungry, he’d grab anything left over from the previous meal to make soup or fried rice. “I grew up in a Japanese family, and I was taught to never waste anything,” Nakajima says. This soup is his riff on a recipe from his mother. Add milk for a creamier texture, or more dashi for a thinner consistency. Substitute any mashed vegetable you have on hand, such a cauliflower or sweet potato, but be sure to finish the soup with generous pats of melting butter and an extra drizzle of soy.

Shota Nakajima
November 2020


Photo by Victor Protasio / Food Styling by Torie Cox / Prop Styling by Claire Spollen

Recipe Summary

20 mins
4 hrs


Ingredient Checklist


Instructions Checklist
  •  Combine onion, celery, and 2 1/2 cups dashi in a small Dutch oven. Bring to a boil over medium-high. Reduce heat to medium-low, and simmer, uncovered, stirring occasionally, until vegetables are tender, 35 to 40 minutes.

  • Add leftover mashed potatoes to dashi mixture, and whisk until well combined. Stir in milk, if desired, for a creamier texture. Stir in remaining 1 cup dashi, 1/4 cup at a time, to thin soup to desired consistency. Cook over medium-low, stirring occasionally, until warm, 4 to 6 minutes. Season with salt and pepper.

  • Top servings with butter and drizzle with soy sauce. Garnish with mitsuba or celery leaves.

Make Ahead

Soup can be prepared up to 3 days in advance and stored in an airtight container in refrigerator. Reheat over low, stirring often to prevent simmering.

Suggested Pairing

Aromatic dry Riesling.