In a blender or small food processor blend the garlic paste, the mustard, the lime juice, the mayonnaise, and salt and pepper to taste until the mixture is smooth and with the motor running add the oil in a stream. Blend the mixture until it emulsified, add enough of the water to thin the vinaigrette to the desired consistency, and blend the vinaigrette until it is combined well. In a large bowl toss the romaine with the vinaigrette. Serves 6. Gourmet March 1993