Freshly ground black pepper *Choose avocados that are firm, with just a slight give. If the avocado is soft enough to hold an indentation, it's overripe and won't have the rich nutty flavor that you want for this salad. Bring water to a boil in the bottom of a vegetable steamer. Cut potatoes in half; place them in the steamer basket. Cover and steam until they are cooked through, about 20 minutes. Remove the potatoes from the heat and allow them to cool slightly. While potatoes are cooking, whisk oil and vinegar together in a large bowl. Season to taste with salt; set aside. When potatoes are cool enough to handle without burning your fingers, cut them in 3 cm cubes. Toss them in the oil and vinegar so they are coated well, and set them aside to cool to room temperature, tossing occasionally. In a small bowl, whisk together the sour cream, yogurt and horseradish. Mince the dill and add it to the sour cream mixture, stirring well. When potatoes have cooled to room temperature, add celery and toss to combine. Then add the sour cream mixture; toss again. Halve, pit and peel the avocados. Cut them into 3 cm cubes; place in a small bowl with the lime juice. Toss so the cubes are moistened with the juice. Then add the avocados, with all of the lime juice, to the potatoes; toss gently until they are well distributed and coated with the dressing. Add pepper and additional salt to taste, and either serve immediately or chill for 30 minutes and then serve. While Loomis says that this salad does not keep well and shouldn't be counted on for leftovers, she says that it's one of the most popular potato salads she's ever made. Yield: 6 to 8 servings. From _Farm House Cookbook_ by Susan Herrmann Loomis. New York: Workman Publishing Company, Inc., 1991. Pp. 267-268. ISBN 0-89480-772-2. Electronic format by Cathy Harned. Submitted By CCH@SALATA.COM (CATHY HARNED) On 14 JAN 96 090105 -0800