Tonight, it's the last quarter-final, and the week's best chefs return to do battle once more. They all want a place in knockout week, but to get there they'll have to impress the judges, as well as some special guest diners who might just know a thing or two about food.It's the invention test first, and this time the judges would like a dish centered around beetroot. They can raid the larder for anything they like, as long as the beetroot is shown off in its best light. This is one vegetable that lends itself just as well to sweet dishes as it does to savoury ones, so creativity should be off the chart.The infamous critics challenge comes next, which might have even the most seasoned chefs looking towards the exit. Hoping for some mind-blowing plates of food tonight are Leyla Kazim, Grace Dent and Jay Rayner. This is a real chance for the contenders to cement themselves in the minds of these influential diners.Those that impress the most will nab one of the last few places in knockout week, and still be in with a shot at becoming MasterChef: The Professionals champion 2024.