It's quarter-final time, and that can only mean more pressure for this week's most talented professionals as they return to the kitchen ready to battle for a place in knockout week. Getting there will require oodles of creativity, as well as the perseverance to impress their toughest critics yet.The invention test is their first stop. The chefs will need to create a standout dish featuring the key ingredient, offal, as the star of the show. The larder has been packed with goodies, including chicken livers, sweetbreads, chicken hearts, tripe and tongue, as well as a broad range of fruit, vegetables, herbs and spices. They will have just ten minutes to develop a dish that will tickle the judges' taste buds, and then 70 minutes to bring their creation to life.The critics round is up next. Jimi Famurewa, Grace Dent and Tom Parker Bowles are back, hoping to sample some exquisite plates of food. Can the professionals reach their high standards, or will the occasion prove too overwhelming?Marcus and Monica will consider the critics' reviews and reward the best chefs with a place in knockout week as the hunt for this year's champion continues.