Place lotus seeds and alkaline water in a large saucepan. Add one litre of water and boil for 6-7 minutes. Drain and wash the lotus seeds in clean water. Rub off the skin and remove the green centres. Soak in water for about 30 minutes (this is to remove alkaline taste in the lotus seeds).
Cook the peeled lotus seeds with 250ml water until soft. Drain the water, then blend the lotus seeds in a food processor with a bit of the boiled water into a fine paste.
Heat a deep nonstick saucepan over a medium-low fire. Add the paste. Stir and cook the paste with the sugar over low heat until thick and almost dry. Mix in durian. Stir until well combined.
Add oil in batches of 2 tablespoons each time. Keep cooking and stirring the paste until it thickens. Stir in the maltose to mix until the paste is really thick and leaves the sides of the pan.
Remove and leave to cool completely. The paste can be chilled in the refrigerator before use for mooncake.