In a large saucepan cook potatoes, covered, in a small amount of lightly salted boiling water until just tender. (Allow 20 to 25 minutes for medium potatoes or 15 to 20 minutes for new potatoes.) Drain potatoes well. Peel and cube potatoes or quarter new potatoes.
In a mixing bowl combine celery, green or red sweet pepper, and onion. Add cooked potatoes. Toss to mix.
For dressing, in a blender container or food processor bowl combine cottage cheese, mayonnaise or salad dressing, 2 tablespoons milk, mustard, and salt. Cover and blend or process until mixture is smooth. Add to potato mixture. If desired, add dillweed, basil, or celery seed. Toss to combine all ingredients. Cover and chill at least 5 hours. If salad seems dry after chilling, stir in 1 to 2 tablespoons milk to moisten. Makes 8 to 10 side-dish servings.