Steps

1. Crack the eggs into a heatproof bowl.
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2. Pierce the egg yolk a few times with a toothpick and lightly whisk the egg whites. (Key tip!) This prevents the egg from exploding and makes it easier to break up the whites.
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3. Loosely cover with plastic wrap and microwave at 600W for 1 minute 20 seconds.
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4. Remove the plastic wrap, mash with a fork, and roughly break up the egg.
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5. Microwave uncovered at 600W for 20 seconds and mash thoroughly. (Key tip!) Heating in two stages results in a texture similar to mashed boiled eggs.
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6. While the egg is still warm, add 1/2 tsp sugar and mix well until dissolved.
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7. Let the egg mixture cool down. (Key tip!) To prevent the mayonnaise from separating, always mix it in after the egg has cooled. To prevent drying, loosely cover with paper towel.
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8. In the 10g salted butter, brought back to room temperature, add the 1/4 tsp mustard and mix well to make mustard butter. (Key tip!) You can omit the mustard for children.
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9. To the cooled egg mixture, add 2 tbsp mayonnaise and salt and pepper to taste, then mix well.
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10. Spread the mustard butter on the inside of 2 bread slices (8-slice thickness). (Key tip!) Spreading butter prevents the moisture from the filling from soaking into the bread. Mayonnaise can also be used as a substitute.
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11. Place the egg mixture on one slice of bread and top with the other slice, pressing lightly.
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12. Wrap tightly in plastic wrap and let it sit for about 5 minutes to meld.
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13. Cut into desired sizes while still wrapped. This completes the basic egg sandwich.
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14. [Arrangement Egg Sandwich] Finely chop 1/8 onion and place it in a container.
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15. Drizzle 1 tsp vinegar over the chopped onion, ensuring it's submerged, and let it soak for about 5 minutes. (Key tip!) Finely chopping and soaking in vinegar effectively removes the sharpness of the onion. If you're sensitive to the sharpness, you can also microwave it for 30 seconds.
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16. To the cooled egg mixture (prepared up to step 7), add the soaked onion, 2 tbsp mayonnaise, and salt and pepper to taste, then mix well.
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17. Toast 2 bread slices (8-slice thickness) in a toaster until golden brown.
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18. Spread the mustard butter (prepared in step 8) on the inside of the toasted bread slices.
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19. On the buttered bread slices, layer 1 slice of sliced cheese, 2 slices of ham, the prepared arrangement egg filling (from step 16), and 1 leaf of lettuce.
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20. Top with the other slice of bread and press lightly.
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21. Wrap tightly in plastic wrap and let it sit for about 5 minutes to meld.
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22. Cut into desired sizes while still wrapped. This completes the arrangement egg sandwich.
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