Step 1 – Preheat oven to 160°C. Grease a 20cm round springform pan and line the base with baking paper.
Step 2 – Place oranges in a large saucepan; cover with cold water. Bring to the boil and cook for 15 minutes. Drain. Return to pan and cover with fresh cold water. Bring to the boil. Cook for a further 15 minutes. Drain and repeat once more or until very tender. Drain. Coarsely chop and discard any pips.
Step 3 – Place orange in a food processor; process until smooth. Use an electric mixer to whisk eggs and sugar until thick and pale. Add orange, almond meal, baking powder, cinnamon and cardamom; gently fold until just combined. Spoon into prepared pan; smooth the surface. Bake for 1 hour or until a skewer inserted into centre comes out clean. Set aside in pan to cool completely.
Step 4 – To make syrup, use a zester to remove rind from orange. Juice orange. Place the juice, sugar and water in a saucepan over low heat. Cook, stirring, for 5 minutes or until sugar dissolves and syrup thickens slightly. Remove from heat. Add orange blossom water and zest. Set aside to cool.
Step 5 – Drizzle the cake with syrup. Cut into wedges and serve with mascarpone.