1 tablespoon rinsed and minced fermented black beans, or 1 1/2 tablespoons
1 tablespoon minced fresh ginger
2 tablespoons rice vinegar
1 tablespoon Dijon mustard
3 scallions, thinly sliced
Salt and freshly ground pepper
Preheat the oven to 350°. Wrap the sweet potatoes in foil and roast for about 35 minutes, or until tender. Let the potatoes cool slightly, then peel and cut them into 1-inch chunks.
Heat 1 tablespoon of the oil in a small skillet. Add the garlic, black beans and ginger and cook over moderate heat, stirring, until very fragrant, 2 to 3 minutes. Remove from the heat and whisk in the vinegar and mustard. Transfer to a bowl and whisk in the remaining 1/2 cup of oil. Stir in the scallions and season with salt and pepper. Gently fold in the potatoes. Serve warm or at room temperature.
The sweet potato salad can be refrigerated overnight.