For the yuzu dressing:
1 Tbs. sugar
1 Tbs. soy sauce
1/2 cup Kewpie mayonnaise, available at H&L Asian Market
1/4 cup yuzu juice, available at H&L Asian Market
Combine the ingredients in a bowl and whisk together.
For the salad:
2 sweet potatoes, about 2 lbs.
2 tsp. canola oil
2 tsp. kosher salt (do not substitute table salt)
2 celery roots (celeriac), about 1½ lbs., any stalks removed and a few leaves saved, for garnish
1 red and 1 green Belgian endive, cut on the bias into bite-size pieces
Preheat oven to 350°F.
Wash the sweet potatoes but do not peel them. Cut them into one-inch cubes and toss in the oil and salt. Spread them out on a rimmed baking sheet and bake for 30 to 45 minutes, or until soft. Remove from the oven, but leave the potato cubes on the baking sheet.
Scrub the celery roots well. Cut off the top and bottom, then the outside rough edges, trimming the tough outer layer off. Cut them into thin slices, preferably using a Japanese mandoline (smaller and less expensive than traditional French models) to make the job easier. Then julienne the slices (cut them into matchstick-size thin strips). Because the celery root will oxidize (turn darker in color as it’s exposed to oxygen), toss it with the dressing immediately. The dressing will prevent the browning.
Toss the endive and warm sweet potato with the celery root and dressing and garnish with the reserved celery root leaves. Serve immediately.