“Here is a beautiful celebration cake to welcome the newest addition to the royal family – HRH Louis Arthur Charles! This is a real showstopper, as you might expect – rhubarb and custard is a classic combination, and always makes me think of afternoon tea. So, put the kettle on, and dig in! ”
Preheat the oven to 180ºC/350ºF/gas 4. Grease two 20cm springform cake tins and line the bases with greaseproof paper, then dust the sides with flour.
Chop the butter into cubes, then beat with the caster sugar and vanilla until very pale and creamy.
Beat in the eggs one by one, then sift in and fold through the flour and baking powder.
Divide the batter between the prepared tins and spread out evenly. Bake for 25 to 30 minutes, or until golden and an skewer inserted comes out clean. Cool for 10 minutes in the tins, then transfer to a wire rack to cool completely.
Meanwhile, to make the jam, trim the rhubarb, chop into 3cm chunks and place in a large pan with the caster sugar and 2 tablespoons of water. Mix well.
Place the pan over a medium heat with the lid ajar. Bring to the boil, then reduce the heat to low and simmer for 5 minutes.
Remove the lid and simmer for a further 10 minutes, or until the rhubarb has broken down and is thick and jammy, stirring occasionally. Leave to cool.
To make the custard, mix the custard powder, icing sugar and 1 splash of milk together in a pan. Whisk to a smooth paste, then pour in the remaining milk and whisk again until well combined.
Place over a low heat and cook gently for 10 minutes, or until thick and silky smooth, whisking continuously.
Take the custard pan off the heat and cover with a layer of non-PVC clingfilm, making sure it’s in contact with the custard – this will prevent a skin forming on the surface.
To make the buttercream, chop the butter into cubes, place in the bowl of a stand mixer, and whisk for 2 minutes, or until creamy (or beat it by hand).
Sift the icing sugar into a bowl, then gradually add it to the mixer, a few spoonfuls at a time. When all the sugar has been added, whisk for a further 4 to 5 minutes, or until very pale and fluffy – it should resemble whipped cream.
Add 1 small splash of water to the buttercream and fold through to loosen slightly, if needed. Spoon the buttercream into a piping bag with a 1.5cm plain round nozzle, or use a large sandwich bag (then snip off the corner).
Whisk the cooled custard to loosen, then scrape into another piping bag with a 1.5cm plain round nozzle, or use a sandwich bag.
Slice the cooled cakes in half horizontally, using a serrated knife, reserving the prettiest cake half for the top.
Place one cake half cut-side up, and spread over one third of the jam. Pipe small alternating blobs of custard and buttercream around the outside of the cake. Repeat, until the whole of the cake is covered. Do the same with the next two cake layers.
Place the final cake half on top and dust with a little icing sugar to finish. Decorate with some edible flowers, banners, or cake toppers – whatever you like!