This is a beautiful cake - both in flavour and appearance - that puts seasonal blood oranges on full display.
300 gmunsalted butter, softened400 gmcaster sugarFinelygrated rind and juice of 2 lemons and 2 blood oranges255 gmhazelnut meal165 gmfine polenta 6eggs125 gmGreek-style yoghurt, plus extra to serve150 gm(1 cup) plain flour Blood orange topping220 gm(1 cup) caster sugar125 ml(½ cup) blood orange juice2blood oranges, unpeeled, thinly sliced, seeds discarded
For blood orange topping, stir sugar and blood orange juice in a saucepan over medium heat until sugar dissolves, add blood oranges slices and simmer until tender (10-12 minutes). Set aside to cool, then drain, reserving syrup, and arrange orange slices in the base of a buttered 26cm diameter cake tin lined with baking paper. Pour 100ml of the syrup over and set aside.
Preheat oven to 180C. Beat butter, sugar and rinds in an electric mixer until pale (2-3 minutes). Combine hazelnut meal and polenta in a bowl, add half to the butter mixture and mix on low speed to combine. Add eggs one at a time, mixing to combine and scraping down sides of bowl between each addition. Add remaining hazelnut meal mixture, juices, yoghurt and flour, and stir gently to combine. Carefully spoon mixture into cake tin over oranges and syrup and spread gently to cover evenly, smooth top, then bake until golden and a skewer inserted withdraws clean (50 minutes to 1 hour; cover with foil if cake colours too quickly). Set aside to cool briefly (10 minutes), then turn out carefully onto a wire rack to cool to room temperature. Serve with remaining syrup, warmed, and extra yoghurt. It will keep in an airtight container for up to 4 days.