4 pounds baking potatoes, peeled, halved lengthwise, and cut crosswise into 1/2 inch slices
3 cups sliced celery
1/2 cup chopped scallions
1/4 cup minced fresh parsley
1/2 pound sliced lean bacon, cut crosswise into 1/2 inch pieces
1 large egg
5 teaspoons fresh lemon juice
1 tablespoon Dijon style mustard
1/2 teaspoon salt
1/4 teaspoon pepper
1/2 cup vegetable oil
In a kettle cover the potatoes with cold water, bring the water to a boil, and add salt to taste. Simmer the potatoes for 10 to 12 minutes, or until they are just tender when pierced with a fork, and drain them. Transfer the potatoes to a serving bowl and add the celery, the scallions and the parsley. In a skillet cook the bacon over moderate heat, stirring, until it is crisp and transfer it with a slotted spoon to paper towels to drain. Reserve 1/4 cup of the bacon fat and let it cool for 15 minutes. In a blender or food processor blend the egg, the lemon juice, the mustard, the salt, and the pepper for 5 seconds, with the motor running add the oil and the reserved bacon fat in a stream, and blend the mixture until it is emulsified. With the motor running add 1 1/2 tablespoons warm water. Pour the dressing over the potato mixture, add the bacon and toss the salad until it is combined. Sprinkle the salad with salt and pepper to taste and serve it at room temperature. The salad may be made up to 3 days in advance and kept covered and chilled. Serves 6.