1. Preheat the oven to gas 3, 170°C, fan 150°C. Line a deep 23cm spring-form round cake tin with baking paper.
2. Spoon the ginger preserve onto the base of the cake tin. Cut the rhubarb into lengths – vary the size to fit the base of the tin and arrange on top in a single layer.
3. Zest the orange into a large mixing bowl, add 180g of sugar, the flour, baking powder, ground almonds, eggs, 180g of yogurt, 80ml of neutral oil (such as olive or sunflower) and a pinch of sea salt. Whisk together until smooth, then pour over the rhubarb.
4. Bake in the oven for 45 mins to 1 hr until golden and a skewer inserted comes out clean. Remove and allow to cool in the tin for 10 mins, then carefully release from the tin.
5. Meanwhile, to make the orange syrup, juice the orange into a small saucepan and pop over a low-medium heat with 1 tbsp of sugar. Heat gently until the sugar has dissolved, simmer for a couple of mins until thickened and syrupy.
6. Gently top the cake with an upturned plate and carefully flip over, then peel away the baking paper. Drizzle over the orange syrup.
7. Leave to cool slightly before slicing and serve with a dollop of Greek yogurt, if you like.
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