Place ranch dip mix in large mixing bowl. Add enough olive oil to make a dressing like consistency. Add potatoes and toss well to coat.
Place potatoes in oiled 13x9 baking pan. Cover with aluminum foil and place in 425 degrees F oven for 35 minutes or until potatoes are fork tender. Remove from oven.
Add butter/margarine, sour cream and 1 pkg. of Cheese. Mix well and sprinkle remaining cheese on top. Return to oven for 5-10 minutes or until cheese is melted and bubbly. Remove from oven, place in serving bowl and serve immediately.