Rich, creamy and intense, chocolate is for many people the ultimate in gastronomic luxury. However, it can be a tricky beast to handle, making it a fitting challenge for the Great British Bake Off semi-final.

To find out about the challenges facing the four remaining bakers, we asked top pastry chef Charlotte Marrifield, owner of Sugar Therapy and designer of desserts for Gü and Lily O’Brien’s, for her thoughts.

First up, the signature challenge is a deceptively simple chocolate tart.

A wide range of ganaches, mousses, caramels and fruit fillings abound and Marrifield advises those making ganache to be gentle – heating the mixture too much could make it split and beating too vigorously could also make it split or appear dull once set.

The prospect of tempering chocolate may terrify many of the contestants and Marrifield says the unique and unpredictable conditions of the tent, including humidity, could present a real challenge.

“Chocolate can be a real diva and will do what it wants when it wants and even as little as half a degree [in temperature] can make the difference between shiny tempered chocolate or chocolate with a dull bloom,” she says: “They need a good thermometer and popping the chocolate once tempered and formed in a mould or tray into the fridge for five minutes to dry is perfectly acceptable.”

As an added challenge, the pastry will have to be chocolate, which Marrifield says will make it very difficult to roll out, due to the drying effect of the required cocoa powder.

“I would suggest using whole eggs and egg yolk in the dough to enrich it, this will give a richer flavour,” she says.

The pressure ramps up for the technical section as Mary Berry sets the bakers a chocolate soufflé challenge so fast that it requires a staggered start.

Marrifield, however, feels the task is easier than it might at first seem.

“Soufflés are easier than they appear,” she says: “It’s all about timing and getting all the prep done before assembly and making sure the ramekins are greased well enough using upward brush strokes to allow the soufflé to rise.”

This week’s showstopper challenge promises to be real treat, as the contestants must create spectacular chocolate centrepieces. Animals and architecture will feature as the bakers have to produce something which not only looks good but tastes good.

“Chocolate sculptures are an amazing way to show off creativity, but they need to remember timing and patience,” says Marrifield: “Both of these are crucial and freeze spray is always a helpful tool if they are joining pieces of tempered chocolate together.”