Place the large potatoes into a large pot of water and bring to the boil.
Once boiling reduce the heat and allow to simmer for about 5 minutes then add the baby potatoes to the pot and bring back to the boil. Once boiling allow to boil for a further 5 minutes. The potatoes should be just tender.
Drain well then slice the large potatoes in half lengthways.
Place all the potatoes into an oven roasting tray.
Place the butter into a small pot together with the KNORR Creamy Garlic and Herb Salad Dressing and the rosemary and heat until the butter has melted.
Pour the sauce over the potatoes, drizzle liberally with oil and season with freshly cracked salt and black pepper.
Roast in the oven for 45 minutes to an hour turning occasionally until the potatoes are well browned and crispy.