Preheat oven to 200°C.
Using a sharp knife, thinly slice potato without going all the way through.
Pat potatoes dry with paper towel.
Place, cut side up, in a shallow roasting pan.
Combine margarine, oil, garlic, and KNORR Salad Dressing and salt and pepper in a bowl.
Brush mixture over potatoes.
Roast potatoes for 50-55mins, basting ½ way through the cooking time.
Serve with leftovers or roast chicken pieces and vegetables of your choice.