Start with the sponge. Add the unsalted butter, oil and sugar to a stand mixer bowl and, using the paddle attachment, cream together for 6–8 minutes until the butter is aerated, lighter in colour and doubled in volume.

Add the eggs one at a time, mixing well between each addition.

Meanwhile, in a separate bowl, add the flour, baking powder, bicarbonate of soda, ground cardamom and salt. Use a balloon whisk to combine.

Add half of the flour mixture to the stand mixer, along with half the buttermilk and vanilla and lightly mix for a few rotations until there are only a few flour streaks remaining

Remove the bowl from the mixer, add the remaining flour mix and buttermilk and, using a rubber spatula, gently fold through. Make sure you scrape the base and sides of the bowl to ensure everything is incorporated and no flour pockets are lurking in the batter.

Transfer the batter to your lined tray and, using the back of a spoon or an offset palette knife, spread out to create an even layer. Tap the tray on the worktop to remove any air bubbles, before popping into the oven for 23–25 minutes.

Once the top of the sponge is golden and bouncy, remove from the oven and leave to sit in the tray for 5 minutes.

Cover the top of the sponge (still in the tray), with clingfilm and leave to completely cool.

For the roasted compote, turn up the temperature on the oven to 180C Fan/200C/390F.

Chop the rhubarb into 1 inch batons and add to a large baking dish. Go in with the remaining ingredients and mix well until everything is coated and the cornflour has dissolved.

Pop into the oven for 20 minutes, Remove the dish and give everything a mix, before popping back into the oven for another 20 minutes. By now the rhubarb should break down easily when pressed. If so, remove from the oven and leave to cool. If it doesn't, pop back into the oven for a further 5 minutes.

When cool, lightly blitz using a hand blender for a smooth consistency.

Make the soaking syrup by adding everything to a small pan. Give it a mix before placing over a medium heat. Bring to the boil, reduce the heat and continue cooking on a simmer for 5 minutes until thickened to a light syrup consistency. Leave to cool.

When you're ready to stack, make the whipped cream by adding the mascarpone, icing sugar and vanilla to a mixer bowl. Use the whisk attachment to mix until smooth.

Pour in the double cream and mix until you just reach medium peak. Don't mix more than this otherwise your cream will curdle.

To construct, divide the sponge into 3 along the long edge. Place one sponge onto your serving plate.

Generously bathe the top with the vanilla sugar syrup.

Add a generous layer of whipped mascarpone on top, before piping a thick border of cream around the edge. Fill the inside with half of the roasted rhubarb berry compote.

Carefully place the second sponge on top, repeating the syrup, cream and compote process.

Top with the final sponge, before using half the remaining cream to crumb coat. Pop in the fridge to set for 45 minutes before using the remaining cream to decorate as you wish.