When cool, tip the sweet potatoes into the bowl of a food processor. Drizzle over the garlic infused olive oil and tahini and squeeze over the juice from the lemon. Blitz for a minute, to a chunky puree. Keeping the motor running, slowly add 60-80ml of cold water and blitz until you have a silky smooth consistency. Spoon the hummus into a serving bowl, drizzle with a little extra olive oil and sprinkle over the zaatar and a few extra chilli flakes, if you like.