Go back in time to the wacky and wonderful Seventies with this visually striking, and cocktail-inspired, shag-pile cake. Made with coconut flour, the sponge is naturally gluten-free and sandwiched with a sticky pineapple jam, covered in a lime meringue buttercream.
Heat the oven to 180°C/160°C fan/350°F/Gas 4. For the sponges, place the coconut flour, baking powder, sugar and salt in a large mixing bowl and mix well with a spoon.
In a separate bowl, whisk the eggs, vegetable oil, vanilla paste and coconut extract together. Pour the mixture into the flour mixture and, using an electric hand whisk, whisk to a smooth batter.
Divide the batter equally between the three sponge tins (they should be about three-quarters full) and level the batter with a palette knife. Bake for 25–30 minutes, until slightly risen and a skewer inserted into the centres comes out clean. Remove from the oven and transfer to a wire rack to cool in the tins for 5 minutes, then turn out and leave to cool completely.
While the sponges are baking and cooling, make the pineapple jam. Place the pineapple chunks, lime juice, jam sugar and pectin into a large heavy-based saucepan set over a medium heat. Stir to dissolve the sugar, then cook for 35–40 minutes, until the mixture is syrupy and slightly caramelised. Remove from the heat and leave to cool.
Make the meringue buttercream. Put the egg whites, sugar and salt into a medium, heatproof bowl set over a pan of simmering water. Using an electric hand whisk, whisk for about 5–10 minutes, until the mixture thickens, increases in volume, turns from opaque to bright white, and leaves a ribbon trail when you lift the whisk.
Pour the mixture into the bowl of a stand mixer fitted with the whisk and whisk on medium–high speed for 3–4 minutes, until the mixture doubles in volume and is thick, stiff, glossy and cold to the touch.
Switch to the beater attachment. Gradually, add the softened butter, beating continuously until smooth. Add the lime juice and mix again to combine. Spoon one quarter of the meringue buttercream into the piping bag fitted with the round nozzle. Divide the remaining meringue buttercream between six bowls and colour each bowl using the yellow, green, blue, dark red and purple food-colouring pastes. Spoon each colour into a piping bag fitted with a grass nozzle.
Pipe dots of the plain meringue buttercream onto a cake plate or stand, using the buttercream in the piping bag fitted with the round nozzle. Place one of the sponges on top and pipe a ring of buttercream around the top edge. Fill in the middle with half the pineapple jam. Place a second sponge on top, then pipe a ring of buttercream around the edge and fill in the middle with the remaining jam.
Spread the top and sides of the stacked sponges with a thin, even layer of uncoloured buttercream to create a crumb coat, then chill the cake for 30 minutes.
Remove the cake from the fridge. Pipe the yellow, green, blue, dark red and purple-coloured meringue buttercreams in a wacky and wonderful pattern to decorate – like a multi-coloured shag pile carpet.