Peel and halve or quarter the potatoes, if large, so they’re all the same size. Put in a large pan and cover with cold water and a pinch of salt. Add one half of the garlic bulb. Bring to a simmer and cook for 10 mins until a knife goes easily through the potatoes, then drain well, reserving the garlic. Leave the potatoes to steam-dry in the pan for 10 mins. Heat the oven to 220C/200C fan/gas 7.
Pour the oil into a large baking tray or two smaller ones – it should cover the base of the tray, so add a little more if you need to. Heat in the oven for 10 mins until really hot. Carefully transfer the spuds to the oil, leaving lots of room between each one (otherwise they will steam, rather than roast) and coat in the oil, taking care not to splash yourself. Season, then add both halves of the garlic, blanched and not, and nestle the bay leaves underneath the spuds.
Roast for 40-45 mins, turning halfway through and coating in more oil, until golden and crunchy. Season with more salt and pepper, and zest the lemon directly over the potatoes so the essential oils spritz over the spuds. Serve with the roasted garlic in its shell.