Place whole oranges in medium saucepan, add enough hot water to cover oranges. Cover, bring to boil, then simmer about 2 hours, or until oranges are tender. Replenish water with boiling water as it evaporates during cooking. Drain oranges, cool; discard water.

Preheat oven to 160°C (140°C fan-forced). Grease deep 20cm round cake pan; line base with baking paper.

Process almonds and sugar until almonds are roughly chopped; transfer mixture to medium bowl.

Quarter whole oranges, blend or process until smooth. With motor operating, add eggs one at a time, process until combined. Add almond mixture, baking powder and extract, process until just combined. Spread mixture into pan.

Bake cake about 1 hour.

To make lime syrup; stir ingredients in small saucepan over heat, without boiling, until sugar dissolves. Simmer, uncovered, without stirring, about 5 minutes or until slightly thickened.

Pour hot syrup over hot cake. Stand cake in pan 30 minutes. Turn cake onto wire rack over tray. Serve warm or cold.