The secret to restaurant style ranch dressing are the ingredients. You can't use just any type or brand of mayonnaise or any type or brand of ranch powder. You have to use McCormick Mayonesa and Restaurant Style Hidden Valley Ranch powder. And, do not use regular milk. It must be buttermilk. While make substitutions will still result in a good ranch dressing, it won't be the restaurant style that you are looking to make at home.