Rosemary salt roast potatoes

1. Preheat the oven to 50˚C, gas mark ¼, or as low as your oven can go. Put ²⁄ ³ of the rosemary leaves in a small blender or food processor with the salt. Pulse until the rosemary is obliterated and the salt has turned green. Spread over a baking tray and dry in the oven for 30 minutes – it should be moisture-free and caked together. Return to the blender or processor and give it a quick pulse. Store at room temperature in an airtight container until needed.

2. Meanwhile, peel the potatoes and cut into 5cm pieces. Put in a large pan and fill with cold water, 1 tsp rosemary salt, the garlic and remaining rosemary sprigs. Bring to the boil and simmer for 10-15 minutes, until you can tease a fork fairly easily through the outside of the potato but still meet resistance towards the middle. Drain and cool; shake to roughen up the edges. (This can be done a few hours ahead.)

3. Preheat the oven to 220˚C, gas mark 7 (ideally; or the same as for roasting your meat). Pour the oil into a roasting tray on the hob and heat to near smoking point. Carefully add the potatoes, turning them over in the hot oil so they are glossy, then put on the top shelf of the oven and cook for about 1 hour until crisp and golden, giving the tray a shake after 30 minutes. When ready to serve, remove from the oven and season with the remaining rosemary salt.