Place the oranges in a medium sauce pan can cover them with cold water.

Place the pot over high heat and bring to a boil, reduce the heat to medium and cook the oranges for 15 minutes or until tender.

Drain, then cover the oranges with more cold water, bring to a boil, and cook for another 1 hour and 45 minutes, checking the water level as it cooks and top it up with boiling water when necessary.

Preheat the oven to 338°F (170°C). Lightly grease and line an 8-inch (22 cm) round spring-form tin with nonstick parchment paper.

Place the oranges into a food processor and process until smooth.

Place the eggs and sugar into a large mixing bowl and beat with an electric mixer until pale and thick.

Gently fold in the pureed orange, okara, and baking powder until just combined.

Pour the batter into the prepared cake tin.

Remove from the oven and let stand in the tin for 15 minutes to cool.

Meanwhile, make the orange syrup. Use a zester to remove the rind from the orange, or use a vegetable peeler to peel the rind from the orange, then use a small knife to scrape the white pith from the peel skin, then juice the orange.

Place the rind in a small saucepan, cover with boiling water, and cook over medium heat for 5 minutes or until soft (this will remove the bitterness from the skin), then drain.

Return the cooked peel to the pot, add the orange juice and sugar, place over low heat, and cook, stirring, for 3-4 minutes or until the sugar dissolves and the syrup thickens.

While the cake is still warm and still in the tin spoon the syrup over the top.

Remove the side of the tin and allow the cake to cool completely, then transfer to a serving plate.