Preheat the oven to 220-230 C, Fan 200-210, Gas 7. Put the potatoes into a large pan of cold, salted water and bring to the boil. Simmer for 5 minutes, then drain.
Pour the olive oil into a roasting tin and heat over a moderate heat with the garlic for about 5 minutes until the garlic has taken on some colour and flavoured the oil. Remove the cloves with a slotted spoon and set aside.
Toss the potato chunks in the hot oil and add the lemon zest. Roast the potatoes in the oven for about 25 minutes before adding the reserved garlic cloves and sage leaves.
Roast for another 20 minutes until the potato chunks are fragrant, crisp and golden. Eat at once as side or see introduction.