In a steamer set over boiling water arrange the boiling potatoes, top them with the sweet potatoes, and steam the potatoes, covered, for 10 to 12 minutes, or until they are just tender. Transfer the potatoes to a bowl and let them cool. In another bowl whisk together the vinegar, the mustard, and salt and pepper to taste, add the oil in a stream, whisking, and whisk the dressing until it is emulsified. Add the dressing to the potatoes with the onion, the bell pepper, and the gherkin and combine the salad well. Serves 6.

Gourmet July 1991 Converted by MC_Buster. Converted by MM_Buster v2.0l.