Bring a pan of well-salted water (1 teaspoon of salt to a litre of water) to the boil.
Peel the potatoes and cut them into a 2-2.5cm (¾-1") dice. Parboil the potatoes in the salted water for 5 minutes, then drain and allow to steam dry for 5 minutes.
Whilst the potatoes are steam drying, place the beef dripping in a baking tray in the oven at 200°C or 400°F.
Dice the garlic as finely as you can and place it in a bowl.
Pick the leaves from the rosemary and chop them as finely as you can.
Add the potatoes to the tray with the beef dripping, season with salt and pepper, and then stir to coat the potatoes with the fat. Return to the oven and cook for 15 minutes.
Remove the potatoes from the oven, sprinkle over the garlic and rosemary, stir and return them to the oven for 10 minutes.