If you want to get organised, prep these ahead to the end of step 2, then cover until needed.
Method
Pick the sage leaves into your largest roasting tray, then use a speed-peeler to strip in the lemon peel, and squeeze in the juice. Drizzle in 2 tablespoons of olive oil, add a pinch of sea salt and black pepper, then break apart the unpeeled garlic bulb into the tray.
Scrub the potatoes, then cut into 1cm-thick slices. Working in batches, place on a large screaming-hot griddle pan for a couple of minutes on each side, pressing them down with a fish slice until beautifully bar-marked, and transferring to the roasting tray as you go. Toss together, then spread out in a single layer.
Preheat the oven to 200°C/400°F/gas 6. Roast the potatoes, uncovered, for 45 minutes on the top shelf, or until cooked through and lightly golden. Squeeze the soft garlic cloves out of their skins, to serve.