1. Bring a large saucepan of water to a gentle boil. Gently lower the eggs into the boiling water and reduce the heat. Cook at a gentle simmer for 6 minutes.
2. Meanwhile, prepare 2 bowls of iced water.
3. After 6 minutes, remove 2 eggs with a slotted spoon and transfer them to one bowl of iced water. This will yield creamy, soft-yolk eggs.
4. Continue cooking the remaining eggs for another 6 minutes, then transfer the eggs to the other bowl of iced water.
5. Gently crack and peel the 2 soft-yolk eggs. Set them aside.
6. Now crack and peel the remaining 6 eggs. Place them in a large bowl and mash them roughly with a fork to about 1/4-inch pieces. You could also chop the eggs with a knife and transfer to a bowl.
7. Add the mayonnaise and sambal belacan to the bowl of eggs and fold with a rubber spatula so everything is mixed in evenly.
8. Slather butter on one side of each slice of bread.
9. With a sharp knife, cut the soft-yolk eggs into halves lengthwise. Sprinkle a little sea salt over each half.
10. Place each half on the centre of a slice of buttered bread, laying them yolk-side down.
11. Divide the egg salad among the sandwiches, placing about a quarter cup of egg salad, on top of and around the soft-boiled egg half. Using a butter knife, spread the egg salad evenly towards the crusts in all directions until the bread is covered.
12. Top with the remaining slices of bread, butter-side down.
13. Using a serrated knife, carefully slice the crusts off each sandwich.
14. Cut sandwiches into halves (slicing against the soft-yolked egg half breadth-wise) to reveal a pretty cross-section. Serve immediately or refrigerate, wrapped in cling film, for up to 24 hours.