In a large saucepan combine the potatoes with enough cold water to cover them by 1 inch and simmer them, covered, for 10 to 15 minutes, or until tender. Drain the potatoes, let them cool completely, and cut them into 1/4-inch-thick slices. In a kettle of boiling water cook separately the haricots verts, the squash, and the carrots for 3 to 5 minutes each, or until each vegetable is crisp-tender, transferring them as they are cooked with a slotted spoon to a bowl of ice and cold water to stop the cooking. Transfer the vegetables with the slotted spoon to paper towels and pat them dry. In the kettle of boiling water cook the radishes for 2 to 3 minutes, or until they are crisp-tender, and transfer them with the slotted spoon to the bowl of ice and cold water. Drain the radishes and pat them dry. Transfer the vegetables to 5 separate bowls and chill them, covered. The vegetables may be cooked 1 day in advance and kept covered and chilled.
Make the vinaigrette: In a blender or food processor blend together the shallots, the garlic, the mustard, the lemon juice, the vinegar, and salt and pepper to taste until the mixture is smooth, with the motor running add the oil in a stream, and blend the dressing until it is emulsified. Divide the vinaigrette evenly among the 5 bowls, toss each vegetable to coat it with the dressing, and arrange the vegetables decoratively on a large platter.
adapted from a recipe courtesy of Gourmet Magazine