1. Clean and shell preserved egg then rinse and dry. Dice egg and arrange on a shallow heatproof dish.
2. Beat fresh eggs very lightly in a bowl. Separate salt egg. Add its white to bowl; then dice its yolk and add.
3. Heat (but do not boil) stock. Slowly stir stock into fresh-and-salt-egg mixture, along with peanut oil and salt. Pour over diced preserved egg.
4. Steam over low heat until eggs are set and custard-like (15 to 20 minutes).
5. Mince scallion; sprinkle over the top.