Preheat the oven to 170°C.
Grease a 23cm round springform cake tin with the sunflower oil and place on a baking sheet.
For the caramel, put 225g of the granulated sugar into a small, wide, heavy pan on a low heat.
Without stirring, let the sugar dissolve completely.
Once liquid, let it gently bubble for 15–20 mins or until it is a deep golden colour.
Add 10g of the butter, half the vanilla extract and the salt, gently swirling the pan to combine the butter as it melts.
Once fully incorporated, immediately remove from the heat and pour the caramel into the prepared cake tin.
Place the plum halves on top, cut side down, nestled tightly together, and set aside.
In a large mixing bowl, beat the remaining butter together with the remaining granulated sugar and the brown sugar until pale and creamy: this will take 2–3 mins using a handheld electric whisk; if you don’t have one, use a wooden spoon.
Add the eggs one at a time, beating well.
Once the eggs are well combined, add the remaining vanilla extract, the corn our, ground almonds, our and baking powder to the bowl and fold through with a metal spoon until just combined (taking care not to over-mix), then pour over the plums.
Smooth over the top, then bake for 40–45 mins until cooked through: a thin skewer inserted into the centre of the cake should come out clean.
Transfer the cake to a wire rack and leave to cool in the tin for 5 mins before turning out onto a serving plate.
To do this, put the serving plate on top of the tin and tip over before releasing the sides of the tin and removing the base.
Let the cake cool for a further 5 mins before slicing.
Extracted from Together: Our Community Cookbook (Ebury Press, R455). Photography by Jenny Zarins