Preheat the oven to 180°C.
Cut the bacon into long, thin slices.
Cut the rosemary into 1 cm pieces.
Lay a potato between the handles of two wooden spoons. Using a knife, carefully cut vertical slices down into the potato (the spoons will stop cutting all the way through the potato). Repeat with the remaining potatoes and place them in a roasting dish.
Mix the oil or melted butter with the garlic. Add some pepper. Brush the potatoes, including the slits with the mixture.
Tuck the rosemary and bacon into the slits, alternating. Season with pepper.
Place the dish in the oven and roast for about 45-55 minutes.
Check with a skewer, whether the potatoes are cooked through - if not, cover with foil and bake for another 10-20 minutes, until the potatoes are tender.