Line 23 x 5 cm square cake tin with parchment paper, leaving some overhang. Preheat oven to 170°C.
Stir eggs, sugar, salt and tapioca till evenly mixed. Knead and wring pandan leaves in mixture till completely crushed. Add coconut milk and water. Mix thoroughly. Discard pandan leaves.
2 eggs, 300 g sugar, ⅙ tsp salt, 1 kg grated tapioca, 4 pandan leaves, 375 ml undiluted freshly squeezed coconut milk, 125 ml water
Pour batter into cake tin, moving stream of batter around tin as you pour. Smooth the top, stirring liquid that may accumulate around edges so that batter is evenly mixed.
Bake for about 1¼ hours, till top is golden brown, edges are crusty and slightly caramelized, and inserted skewer comes out almost clean. Cover edges with foil during last 30 minutes if top doesn't brown evenly. Do not over-bake or cake will be dry.
Remove cake from oven. Leave on wire rack till slightly firm, 30-45 minutes. Unmould and leave cake on wire rack till cold, another hour or so. Cut with oiled knife. Serve.
Leftovers should be wrapped and refrigerated. Rebake till thoroughly heated and soft.