Inspired by Loriea’s Week One showstopper, this lightly spiced chilli-and-chocolate sponge is sandwiched with mango jam and topped with a rum-flavoured buttercream to transport us to the shores of the Caribbean.
Heat the oven to 170°C/150°C fan/325°F/Gas 3.
Make the cake. Melt the chocolate with the milk either in a heatproof bowl over a pan of barely simmering water or in short bursts in the microwave. Add the espresso powder and stir until smooth.
Beat the softened butter and caster sugar together using a stand mixer fitted with the beater attachment, on medium speed for 2 minutes, until the mixture is pale and smooth.
Add the eggs a little at a time, mixing to combine between each addition.
Sift the flour, cocoa, chilli powder, bicarbonate of soda and baking powder into the bowl. Add the buttermilk and chocolate mixture and mix on low–medium speed until just combined. Scrape down the sides of the bowl and continue to mix on medium speed for a further 1 minute, until the mixture is smooth.
Divide the mixture equally between the prepared cake tins and spread level. Bake for 20 minutes, until the cakes are risen, springy to the touch, and a skewer inserted into the centres comes out clean. Cool in the tins for 2 minutes, then carefully turn out onto wire racks, remove the lining paper and leave to cool completely.
Meanwhile, prepare the fillings and buttercream. To make the mango jam, tip the mango pulp into a small pan and add the jam sugar and grated ginger. Stir over a low heat until the sugar has dissolved, then increase the heat and gently boil for about 3 minutes, stirring from time to time, until the mixture has reduced and thickened to a loose jam consistency. Spoon into a bowl, stir in the lime juice, leave to cool completely, then cover.
Make the ganache. Heat the cream in a small pan over a low–medium heat until just boiling. Place the chocolate in a small, heatproof bowl and pour over the hot cream. Leave for 1 minute, then gently stir until smooth. Continue stirring for 30 seconds, until the ganache starts to thicken slightly, then cover, and chill until needed.
Make the buttercream. Place the egg whites, caster sugar and salt in a heatproof bowl over a pan of simmering water. Using an electric hand whisk, whisk continuously for about 3 minutes, until the mixture is hot to the touch, has turned glossy white and has doubled in volume. Pour the meringue mixture into the bowl of a stand mixer fitted with the whisk attachment, and whisk on medium–high speed for about 5 minutes, until thick and completely cold.
Add the softened butter a little at a time, whisking well between each addition, until you have incorporated all the butter and the buttercream is smooth. Add the vanilla and rum and whisk to combine. Cover and set aside until needed.
Once the cakes are cool, spoon 3–4 tablespoons of buttercream into a piping bag fitted with a medium plain nozzle. Place two cake layers on the work surface and pipe a neat ring of buttercream around the top edge of each cake.
Fit another piping bag with the second plain nozzle and spoon in the ganache. Pipe a 1cm-wide ring inside the ring of buttercream on each cake. Set aside the remaining ganache in the piping bag.
Reserve 1 tablespoon of the mango jam and use the remainder to spread equal layers of jam in the centre of the ganache rings on each cake.
Place one of the topped cake layers on a serving plate and top with the second. Gently press the third (naked) cake layer on top. Spread one third of the remaining buttercream thinly and evenly over the top and sides of the cake to make a smooth crumb coat and chill for 30 minutes until firm.
Spoon 3–4 tablespoons of Swiss meringue buttercream into the piping bag fitted with the star nozzle and, using a palette knife or the cake scraper, coat the sides and top of the cake with the remaining buttercream in the bowl.
Pipe a decorative ring of buttercream around the top edge of the cake. Spoon the reserved jam into the disposable piping bag, snip the end and pipe little blobs of mango jam into the gaps. Pipe a circle of ganache dots around the inside edge.
To decorate, peel and thinly slice the mango, toss the slices in the lime juice and arrange on top of the cake. Scatter with lime zest to finish.