Boil 250ml of water and steep rinsed blue-pea flowers for 5 minutes.
Press liquid from flowers into the pan, discard flowers, and cool the liquid.
Soak half the rice in water and half in blue liquid for 4 hours or overnight.
Juice pandan leaves and strain to reserve the liquid.
Whisk eggs and sugar until fluffy, add salt, pandan juice, and coconut milk.
Heat mixture over low heat for 20 minutes until thickened, then cool and chill.
Drain both portions of soaked rice.
Combine 125ml coconut milk with each rice portion and season remaining milk with salt.
Steam white and blue rice portions in separate lined pans for 20 minutes.
Add salted coconut milk to rice and steam for another 10 minutes.
Press alternate spoonfuls of rice into a lined tin and cool completely.
Serve sliced rice cakes with the coconut pandan custard.