Step 1

Preheat your oven to 200℃ fan/220℃/Gas Mark 7.

Step 2

Put the potatoes into a saucepan pan of cold salted water, pop on the lid, bring to the boil and cook for 10 minutes, until just starting to soften.

Step 3

Meanwhile, pour 60ml (about 4 tablespoons) of the oil into a large roasting tray (or disposable foil tray) and place in the oven to heat up.

Step 4

Drain the potatoes and put back into the hot saucepan to dry for about 5 minutes.

Step 5

Add the remaining oil to the potatoes, along with the onion granules and sea salt. Put the lid back on the pan and give them a really good shake.

Step 6

Carefully tip the potatoes into the hot oil in the tray. The oil should be so hot that when you drop the first potato in you can hear it bubbling. Toss quickly until they are well coated (so the oil doesn't have time to cool) and roast in the oven for about 1 hour until golden and crispy all over (I always allow at least 1 hour 15 minutes).

Step 7

Follow the method above, but only bake for 45 minutes-1 hour. They should be almost done but not quite crispy enough to serve. Leave to cool, cover and place in the fridge overnight.

Step 8

To finish them off the following day, cook for 15-30 minutes until golden and crispy (this can take a while as the potatoes will be cold from the fridge).

Step 9

Follow the method above until the end of step 5 (do not heat the oil at step 3). Leave to cool, cover and place in the fridge until you're ready to roast. Heat the oil as per step 3 and follow the rest of the method.

Step 10

Follow the method above until step 5 (do not heat the oil at step 3). Put the potatoes on a tray lined with baking paper and freeze uncovered, making sure the potatoes are not touching for at least 1 hour. Once they have hardened, you can transfer them into a freezer-safe container (this extra step might seem annoying but it stops the potatoes sticking together.) You can keep them frozen for up to 1 month. Defrost them overnight in the fridge, heat the oil as per step 3 and follow the rest of the original method.