Arugula, Sweet Potato, and Walnut Salad with Dashi &quotVinaigrette&quot

Ingredients

• 1 pound sweet potatoes in jackets, poked all over with a fork
• 1 cup walnut halves, crumbled
• 2 tablespoons extra-virgin olive oil, plus more for drizzling
• 2 cups cold water
• 1/4 ounce dried kombu
• 1/4 ounce dried bonito flakes
• 2 tablespoons soy sauce
• 4 cups arugula
• Kosher salt and freshly ground black pepper

Directions

1. Cook the sweet potatoes in the microwave until they are soft enough to pierce easily with a fork, about 5 minutes. Put them aside until they are cool enough to handle. Peel off and discard the jackets if you like, then cut the sweet potatoes into medium cubes and leave them to cool to room temperature.
2. While the sweet potatoes cool, put the walnuts on a microwave-safe plate. Drizzle with just enough olive oil to give them a light coating, toss thoroughly, then spread them out in one even layer. Microwave on high power in 1-minute bursts, stirring the walnuts after each interval, until they smell toasted and nutty, about 3 minutes. Set them aside to cool.
3. In a medium saucepan, combine the water and kombu. Warm over medium heat until the liquid is almost, but not quite, simmering. Use tongs to lift out the kombu and discard it. Take the pan off the heat, stir in the bonito flakes, and steep for 10 minutes. Pour the dashi through a fine-mesh strainer into a heatproof container, then discard the bonito flakes.
4. In a small bowl, whisk 1/4 cup dashi with the soy sauce to make the shoyu-dashi. Save the remaining dashi for another use.
5. In a clean small bowl, whisk 3 tablespoons shoyu-dashi with 2 tablespoons olive oil. Save the remaining shoyu-dashi for another use.
6. In a salad bowl, add the sweet potatoes, walnuts, and arugula. Pour on the shoyu-dashi and oil dressing, toss until everything is well coated, then season with salt and pepper and serve.