Preheat the oven to 180°C/fan 160°C/gas mark 4. Place the whole garlic bulb on a baking tray and roast for 35-40 minutes.
In a food processor, whizz the chickpeas, tahini, 50ml olive oil and lemon juice together with 2 tbsp warm water until smooth, adding more warm water to loosen a little if necessary.
Unpeel the roasted garlic and squeeze the garlic pulp into the food processor. Whizz again and season to taste. Serve drizzled with extra olive oil and flatbread.