Preheat the oven to 220°C/ 200°C Fan
Cut slices into the potatoes, making sure not to cut all the way through. The slices should be about 3mm apart and go approx 3/4 of the way down through the potato.
Place the potatoes on a baking tray
In a small bowl, mix the melted butter, olive oil, crushed garlic and rosemary
Use a pastry brush to thoroughly coat each potato in the butter mixture, getting it down into the slits. There should be about half of the butter mixture leftover.
Sprinkle salt and pepper over the potatoes (to taste)
Bake for 30 minutes
Remove from the oven and re-brush each potato with the remaining butter mixture
Bake for 20 minutes
Brush the potatoes one last time, using the oil in the bottom of the tray
Bake for another 10-15 minutes or until desired crispiness is reached!