Quick answer: Parboil floury potatoes until the edges soften, rough them up in the colander, then roast in very hot fat (220°C) in a single layer with space around each one. Don't turn them too often.
Crispy roast potatoes come down to surface area and dry heat: a rough, fluffy outside that crisps up, and a hot oven and hot fat to drive off moisture. Get those right and you’ll have a shattering crust every time.
Choose a floury potato
Use a floury variety like Maris Piper or King Edward. They have a fluffy interior that crisps well — waxy salad potatoes (like Charlotte) stay dense and won’t go properly crunchy. Cut them into even, large chunks, around 4–5cm, so they all cook at the same rate.
Parboil, then rough them up
This is the step most people skip, and it’s the most important one.
- Put the potatoes into cold salted water, bring to the boil, then simmer for 8–10 minutes, until the outsides are just soft but the centres still hold.
- Drain well and let them steam-dry in the colander for a minute — dry potatoes crisp, wet ones steam.
- Shake them hard in the colander to rough up the edges. Those fluffy, broken surfaces are exactly what turns golden and crunchy. A light dusting of plain flour or semolina at this stage makes them even crispier.
Use the right fat, and get it hot
Fat matters for both crunch and flavour:
- Goose fat or beef dripping give the crispest, most flavourful results.
- Vegetable, sunflower or light olive oil are great everyday choices.
- Avoid butter on its own — it burns at roasting temperatures.
Heat the fat in the roasting tin in the oven first, until it’s shimmering hot, before the potatoes go in. Cold fat is a classic reason roasties turn out pale and greasy.
Hot oven, and give them space
- Roast at 220°C (fan 200°C, gas mark 7).
- Add the potatoes carefully to the hot fat and turn to coat.
- Spread them in a single layer with gaps between each one. Crowded potatoes steam each other and go soft — use two tins if you need to.
Don’t fiddle
Turn them once or twice during roasting, not constantly. They need uninterrupted contact with the hot tin to form a crust. Roast for 45–60 minutes until deep golden all over. Season with salt as soon as they come out, while the surface is still hot and crisp.
Common mistakes
- Skipping the parboil, or not roughing up the edges.
- Cold fat, or not enough of it.
- Crowding the tin so they steam.
- Salting too early in the process, which can draw out moisture — save it for the end.