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.

November 2020


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

Recipe Summary

4 hrs
20 mins


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.