Preheat the oven to 160 degrees Celsius fan/180 degrees Celsius/350 degrees Fahrenheit/Gas 4.

Start by making the roasted garlic. Place the rosemary, thyme and lemon zest strips in a roasting pan and put the four whole garlic bulbs on top of the herbs. Drizzle the bulbs with a good drizzle of olive oil and season with salt and pepper. Roast in the preheated oven for 25–30 minutes until the bulbs feel soft inside when you press them. Leave to cool.

Once the garlic bulbs are cool, cut them in half with a sharp knife and squeeze out the garlic, which will be creamy and paste like. Discard all of the garlic skins, making sure that no skin is left in the garlic paste. Reserve some of the roasted thyme to garnish the soup and discard the other herbs and the zest.

For the soup, heat the olive oil in a saucepan over a medium heat and fry the onions in the oil until soft and translucent and starting to caramelize. Add the garlic purée and cook for a few minutes more. Add the brandy and cook until it is almost evaporated, then add the stock and lemon juice, bring it to a simmer and then cook over a low heat for about 10 minutes.

Using a stick blender, blender or food processor, blitz the soup until smooth. Taste and adjust the seasoning, and then serve in bowls with the reserved sprigs of roasted thyme to garnish.