01 - Preheat oven to 350°F. Grease and line a 9-inch round springform pan with parchment paper.
02 - Place whole unpeeled oranges in a saucepan, cover with water, and simmer for 30 minutes until very soft. Drain, cool, halve, remove seeds, then blend oranges (peel included) into a smooth purée.
03 - In a large bowl, whisk eggs, sugar, oil, and vanilla until light and frothy.
04 - Stir in the orange purée and lemon zest until fully incorporated.
05 - In a separate bowl, mix ground almonds, baking powder, spices, and salt. Fold into wet ingredients until just combined.
06 - Pour batter into prepared pan. Sprinkle with flaked almonds if using. Bake for 45–50 minutes until a skewer inserted into center comes out clean. Cover loosely with foil if browning too quickly.
07 - Cool in pan for 15 minutes, then transfer to wire rack. Dust with icing sugar before serving.