It's quarter-final time, as this week's six best cooks don their well-earned MasterChef aprons ready to bring their A-game. A place in Knockout Week is now within touching distance, but any slip-ups might cost them the competition.John and Gregg have invited a special guest to set the brief – one of the country's most exciting culinary stars, April Jackson. They will have 90 minutes to deliver a dish that celebrates cheese. April loves everything about cheese, but she wants something that will truly linger in the memory. Every cheese offers its own strength and taste, so this really is a test that will get the amateurs' creative juices flowing. After a total cheese-fest, it's down to the judges to pick their favourites.There's only room in Knockout Week for three, and the lucky ones that make it will be well on the way to MasterChef stardom.