1. Peel lemons and oranges, discard rind, and slice fruit approximately 1/4 inch/5mm thick.
2. Place fruit in a medium sized saucepan with the water, agave nectar and 2 cardamom pods. Cover with a lid and place on a medium heat to simmer for approximately 2 hours until the fruit is totally cooked and broken down, and has a marmalade-like consistency. Take care not to burn as it will become very sticky as it nears the end of its cooking.
3. Preheat oven to 360°F/180°C.
4. Remove the cardamom pods and discard. Stir in the butter to melt and allow mixture to cool.
5. Place fruit into a mixing bowl and mix in the lightly beaten eggs.
6. Stir in the ground almonds, protein powder, bicarbonate of soda, poppy seeds and the flour. Mix well together. It will be quite loose at this point.
7. Line an 8 inch/20cm cake tin with greaseproof paper and a spray of oil. Pour in the cake mixture and bake for 25 minutes until golden and firm to touch.
8. Meanwhile, to make the syrup, warm the lemon and orange juice with the agave.
9. Once cooked, remove the cake from the oven and allow to cool on a cooling wire. Turn it over and place onto your serving plate, brush it with the warm syrup and allow it to soak in.