Dessert chef Christy Tania was once a Thermomix sceptic. Like many of us, she had only seen chefs use the appliance to make dinners and savoury meals. Classically trained in desserts, she found it hard to believe that a machine could handle the intricacies of tasks like tempering chocolate and making choux pastry.

“I knew you could use it to make savoury meals and things like ganache and crème anglaise, but I wondered what else it could do,” says Tania. “I decided to push it and make choux pastry, which is quite temperamental and close to my heart. It went well.” Now she has no less than six of them, finding more uses for them as she goes. Tania makes full use of the machine at her neon-yellow dessert restaurant, Glacé, which opened in Windsor in 2017 and churns out delicacies like an immaculate pandan Swiss roll or a cartoonish raspberry mushroom cake, and even make-at-home curry pastes.

The fraisier cake is a favourite from Tania’s time in France, living near Lyon and studying at the École Nationale Supérieure de Pâtisserie. The French sponge cake is traditionally made in summer when its key ingredient, strawberries, are juicy and ripe (the French word for strawberry is “fraise”).

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“I’ve always loved fraisier,” says Tania. “It’s basically like a strawberry shortcake – a lot of people love it. I like it as a way to finish off a meal.” Tania’s version has a thick layer of silky-smooth vanilla diplomat mousse surrounded by fresh strawberries and sandwiched between two thin génoise sponge cakes. The diplomat mousse is made of crème pâtissière folded through a light Chantilly cream. “It has that bite of custard pastry cream, like in a vanilla slice, but also the clean, light finish of a whipped cream,” she says.

It might sound and look complicated, but Tania says “It’s very easy to make”. Her first tip is that if you’re going to use a Thermomix, actually use the Thermomix – including the Cookidoo element which operates like a built-in digital assistant, telling you when to add ingredients, helping to weigh them and settting time, temperatures and speeds as you work through the recipe. “A lot of people try to use the Thermomix as a [standalone] machine [like a mixer], instead of an assist,” she says. “But you have to make use of [it]. The recipe is right there in the computer and it takes you along step-by-step. Instead of trying to do it by yourself, let the machine do it for you.”

The second tip is based on feedback she’s had that the cake tends to shrink once it’s baked, making it harder to stack and leaving you with a messier finish. To fix this, she suggests baking the cake in a slab instead of in a traditional cake tin. “The trick is to bake it in a big pan in a slab, then cut it into a round shape,” she says. “It won’t shrink, and the cake will have a perfectly sharp edge.” You also don’t need to make it circular – it can be a square cake, or any other shape that you like.

Here’s how to make Tania’s recipe for a summery French sponge loaded with strawberries at home. The fraisier sponge can be made up to 2 days in advance and stored, covered, in the fridge. Remove and decorate 45 minutes before serving.

Recipe: Christy Tania’s Thermomix-friendly fraisier sponge
Serves 8
Prep time: 6 hours, including cooling time
Cooking time: 30 minutes

Butter, for greasing
6 eggs, separated, at room temperature
115g caster sugar
70g plain flour
50g vegetable oil
10–12 fresh strawberries, plus extra to decorate (choose similar sized strawberries, for uniformity)
160g fresh strawberries
Icing sugar, to dust
Edible flowers, to garnish
Acetate (available from cake decorating supply stores, craft stores and office supply shops).

Vanilla diplomat mousse
10g titanium strength gelatine leaves
330g milk
1 tsp vanilla-bean paste
60g caster sugar
25g cornflour
4 egg yolks (approx. 65g)
300g thickened cream

Make the diplomat mousse ahead of time. Place gelatine leaves in a bowl, cover with cold water and set aside to soak until soft and pliable (approx. 10 minutes).

Place milk, vanilla, sugar, cornflour and egg yolks into mixing bowl, then start on Thermomix setting thicken/80°C. Remove gelatine from water and squeeze gently to remove excess water. Add gelatine to mixing bowl and mix on speed 3 for 10 seconds or until gelatine dissolves completely. Pour custard into a bowl, cover surface directly with plastic wrap to prevent a skin from forming. Leave for 1.5 hours or until cool.

Once custard is cooled, add butterfly-whisk insert to Thermomix. Place cream into mixing bowl and whip on speed 3.5 until soft peaks form, watching carefully through hole in mixing bowl lid to avoid overwhipping. Gently fold into cooled custard. Cover the surface of the mousse directly with plastic wrap and refrigerate for 2.5–3 hours or until thick enough to pipe. For the sponge, preheat oven to 175°C. Grease and line the base of 2 springform cake tins (20cm) and set aside.

Insert butterfly whisk in Thermomix. Place egg yolks and 40g of the sugar into mixing bowl, then whip on speed 4 for 5 minutes, or until mixture is pale and fluffy. Remove butterfly whisk and place mixture in a large bowl. Thoroughly clean and dry mixing bowl and butterfly whisk (see tip).

Reinsert butterfly whisk. Place egg whites and remaining 75g of sugar into mixing bowl, then whip on setting 2 min 30 sec/speed 3.5, without measuring cup or until stiff peaks form. Remove butterfly whisk. Gently fold whipped whites into yolk mixture until just combined, taking care not to overmix.

Place a bowl onto mixing bowl lid scale and weigh flour into it. Sieve flour over egg mixture and gently fold until just combined.

Place oil and 50g of the batter into mixing bowl and mix on setting 5 sec/speed 2. Add mixture to batter in bowl and gently fold until just combined.

Divide batter evenly between the 2 prepared tins and bake for 14 minutes, or until a wooden skewer inserted in the centre of each cake comes out clean.

Allow to cool in the tins for 5 minutes, then turn cakes out onto a wire rack to cool completely. Clean and dry mixing bowl. To assemble, cut an 8cm x 63cm strip of acetate, or a double layer of baking paper, and line the side of one cake tin with the collar. Secure ends with tape. Trim the tops of each sponge so they are level. Place one sponge, trimmed side up, in the prepared tin.

Trim the tops of the strawberries to form a flat, level base, then cut in half. Place strawberry halves side by side around the side of the tin, top-side down and with cut-side against the tin. Press them to the acetate or baking paper collar so there are no gaps.

Stir diplomat mousse till it softens, then place it in a piping bag with a plain nozzle (1cm). Pipe a layer of mousse to cover the sponge base and reach halfway up the side of the strawberries. Using a palette knife or back of a spoon, spread mousse in a thin layer up and over the strawberries to fill the spaces in between and cover their tops.

Arrange half the sliced strawberries over the mousse layer, then pipe half the remaining mousse over the sliced strawberries and spread evenly.

Top the layer of mousse with the rest of the sliced strawberries, then pipe over the remaining mousse to cover the strawberries. Spread out evenly so the mousse finishes 1cm below the rim of the acetate or baking paper collar. Place the remaining sponge layer, trimmed side down, over the layer of mousse and press down gently. Cover with plastic wrap and refrigerate for 3 hours, or overnight, to set.

Place fraisier cake on serving plate and gently remove from springform tin, then carefully remove acetate or baking paper collar. Dust the top of the cake generously with icing sugar, then top with extra strawberries and edible flowers before slicing to serve.

Do a vinegar wash to thoroughly clean your mixing bowl before whipping the egg whites. Insert butterfly whisk, then place 500g water and 1 tablespoon of vinegar into mixing bowl and mix for 30 seconds on speed 4. Remove butterfly whisk, empty mixing bowl, rinse with hot water and dry.

This article is produced by Broadsheet in partnership with Thermomix.