Catherine sponge recipe

A passionfruit sponge cake laced with a celebratory kick of real champagne.

This Catherine sponge cake was originally created to celebrate the marriage of Prince William and Kate Middleton. And it includes some of the Duchess of Cambridge's favourite ingredients: passionfruit, marshmallows and champagne. However, champagne is actually quite difficult to include in a cake recipe, as it adds too much liquid. Therefore, to combat this, we've used it in the form of a sticky champagne reduction. Inside the cake there is passionfruit curd and passionfruit marshmallow frosting. The recipe tells you how to make your own passionfruit curd. But if you prefer you can buy a jar of it readymade.

Ingredients

• 150ml Champagne
• 350g sugar
• 1 vanilla pod (optional)
• 300g unsalted butter (at room temperature)
• 6 eggs (medium)
• 200g gluten free flour
• 100g ground almonds
• 1 tbsp gluten-free baking powder
• 1 tsp salt

Passion fruit marshmallow filling:

• 230g caster sugar
• 115ml Champagne
• ⅛ tsp cream of tartar
• 3 egg whites (medium)
• Pinch of Anglesey sea salt
• 55g (about 8 large) white marshmallows
• 2 tbsp milk
• 3 tbsp fresh passion fruit juice (you will need about 4 passion fruits)

Passion fruit curd:

• 3 egg yolks
• 80g caster sugar
• 50ml passion fruit juice (approximately 10 passion fruits or passion fruit juice)
• 35g unsalted butter

Method

1. Preheat the oven to 180°C/350F/Gas 4. Prepare two round baking tins (8-inch/20.5cm) by greasing with a little butter and lining the bottoms with greaseproof paper. Dust with a little flour, then tap to remove any excess.
2. Place the Champagne, 50g sugar and vanilla pod in a small saucepan and slowly bring to boil, swirling the pan until the sugar dissolves. Bring the mixture to boil and simmer over low heat until reduced to about 3 tbsp. Leave to cool while you make the cake.
3. Sift the flour, baking powder and salt into a bowl. Add the ground almonds and stir through gently to combine.
4. Beat the butter and remaining sugar in a large bowl until light and fluffy. Add the eggs a little at a time, beating well with each addition. The mixture should resemble mayonnaise. Using a large metal spoon add the flour and almond mixture, combining gently. Do not overmix. Add the Champagne reduction and mix through.
5. Gently pour the mixture into the prepared pans. Bake for about 20-25 mins until the cake is lightly golden and just set. Allow to cool on a wire rack for a few minutes. Run a clean palette knife around the edges and invert the tin. The cake should release from the tin easily. Leave to cool completely before assembling.
6. For the passion fruit marshmallow filling: In a small saucepan, combine the marshmallows and milk and heat gently, stirring the mixture until the marshmallows are melted. Add the passion fruit juice and stir through.
7. In a heavy saucepan, combine the sugar, cream of tartar and champagne. Swirl gently to dissolve the sugar over medium heat. Once the sugar is dissolved you can boil the mixture until it reaches soft ball (240°C) on a thermometer.
8. Whilst the sugar is boiling, beat the egg whites with a pinch of salt until they form stiff peaks.
9. When the sugar syrup has reached the correct temperature, add the marshmallow mixture and stir through until combined. Put the mixture back on the heat and boil rapidly until it reaches 240°C (soft ball) again. Transfer the sugar mixture into a pouring jug.
10. Place the electric hand whisk in the stiff egg whites and switch on to medium power. Steadily and slowly pour in the syrup. The mixture should go soft, glossy and billowy. Avoid pouring the syrup on the beaters as this will harden the syrup and make the filling go grainy. If the mixture becomes too stiff, just add a little hot water, no more than a teaspoon at a time. Put the mixture in the fridge for 1-2 hrs to firm.
11. To make the passion fruit curd: Strain the egg yolks into a bowl. Add the sugar and the passion fruit juice. Mix well.
12. Pour this into a medium saucepan and cook over a low heat, stirring continuously until the mixture thickens and coats the back of a spoon. The amount of cooking time will depend on the type of saucepan used so allow anywhere from 5-15 mins. Do not allow the mixture to boil or it will spoil. When the thick enough, remove from the heat and whisk in the butter a little at a time. Refrigerate for 1-2 hrs before decorating cake.
13. To assemble: Spread a layer of the passion fruit curd on top of one of the sponges. Add a thick layer of marshmallow filling on top of the curd. Sandwich together with the second sponge. Finish with a sprinkling of icing sugar on top.

Top tip for making this Catherine sponge

Decorate the top of the cake with icing sugar and stencils in the shape of a crown or the Union Jack.

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