Preheat the oven to 200 degree celsius.
Wash and cut the potatoes into thin slices (julienne style). Heat the butter and olive oil together in a non-stick frying pan on a medium flame.
Next, put in the potatoes along with the rosemary, adjust salt and pepper as per taste.
Increase the heat and cook till the potatoes are soft and slightly brown in colour. Keep stirring in between this time.(During this time the potatoes will have settled in the shape of a round and flat pancake.)
Then, transfer the potatoes along with the hot pan into the oven and bake for 30 minutes till the center is soft and the top and bottom is crispy and golden in colour.
Once cooked, remove from the oven and keep on top of paper towels so that excess oil is absorbed.
Then slide it back into a baking tray and cook for another 10 minutes till the top and bottom turn into a deep golden brown colour.
Serve warm by cutting into even slices.