It's quarter-final time, and the week's best chefs are back to fight it out for a place in knockout week. They will need to overcome two daunting tasks to get there, including feeding their toughest audience yet.The first hurdle is an invention test with a difference. The chefs must create a dish that includes tonight's mystery ingredient – garlic. They'll have ten minutes to pick other elements that complement the garlic and just 70 minutes to cook the dish. As well as the more familiar bulbs of garlic, the chefs have a range of garlic to choose from, including tangy black garlic and delicate wild garlic. Whatever they pick, they will need to balance things out – the garlic must enhance the dish, not overpower it.The quarter-final continues with a visit from the formidable critics. Grace Dent, Jimi Famurewa and William Sitwell are on hand to give their view on the chefs' creations as they each dish up two of their best plates of food. It will take something extraordinary to pique the interest of these discerning diners.Once the critics depart, it will be left to the judges to pick the lucky chefs who will move forward into knockout week as the hunt for this year's champion continues.