Heat the oven to 220C/200C fan/gas 7. Pour the oil into one extra-large or two large baking trays and put in the oven to heat up. Remove any eyes on the potatoes and give them a good scrub to clean the skins. Cut into 2cm-thick wedges and tip into a saucepan. Cover with cold water, then add the rosemary and 1 tbsp fine sea salt. Cover with a lid and bring to the boil. Boil for 1 min, then remove from the heat and drain. Leave to steam-dry for 5-10 mins.

Carefully remove the tray or trays from the oven and gently turn the wedges and rosemary in the hot oil. Season, then roast for 50 mins-1 hr, shuffling the wedges around halfway through, until golden and crisp. Meanwhile, heat a dry pan over a medium-high heat and fry the chorizo for 5-6 mins until crispy and the oils have been released. Remove with a slotted spoon and set aside on a plate. You’ll end up with around 2 tbsp oil in the pan (if it looks like much less, add a drizzle of vegetable oil).

Tip the flour, garlic and chilli flakes into the pan and stir to create a paste. Cook for a few minutes before adding the milk, a little at a time, whisking well after each addition. Simmer for 3-5 mins until thickened, then remove from the heat. Stir through the cheese until melted, then season to taste.

Once the potato wedges are golden, tip onto a platter, drizzle over the cheese sauce, and scatter the chorizo over the top, along with the spring onions and parsley.