This is something I often cook for lunch. Even if you’re starting from scratch by making the onsen eggs (which you can also buy at some supermarkets), everything takes a maximum of 45 minutes to prepare. While you need only one egg per serving, I like to cook several at once because it saves a bit of work the next time I want to make this dish; you can store the leftover eggs in the fridge for about a week.
Onsen eggs get their name because in Japan, eggs, still in their shells, are cooked in onsen (hot springs), which have the perfect temperature - usually between 60°C to 80°C (140°F to 175°F) - to cook the egg so the white is gently set and the yolk is still soft. If you don't want to make onsen eggs, you can substitute poached eggs.
Also to save time for future meals, the amount of sizzled spring onions is more than you’ll need for one serving of the noodles; the remainder should be stored in the fridge.
Dried shrimp roe noodles come in small bundles that weigh about 50g (1¾oz). They keep for months in the pantry. One bundle is enough for a light meal, but if you have a large appetite, cook two and mix in a larger amount of the XO sauce and sizzled spring onions. Plain thin Chinese egg noodles can be substituted for shrimp roe noodles.
If you are making onsen eggs, put the eggs in a saucepan that's just large enough to hold them. Add water to cover the eggs by about 2.5cm (1in) then place the pan over a medium flame. Heat until the water is 80°C (175°F), then pour off about one-quarter of the water. Add enough cool water so the temperature is precisely 63°C (145°F) and covers the eggs by 2.5cm ; if needed, reheat the pan until the water is the required temperature. Cover the pan with the lid and leave for 45 minutes, occasionally heating the pan to keep the water at the required temperature. Let the eggs cool to room temperature.
If you don't want to make onsen eggs, substitute poached eggs instead. Pour water to the depth of about 10cm (4 in) in a 25cm (10 inch) wide saucepan. Bring to the boil and add 15ml (1 tbsp) of white vinegar. Crack an egg into a small dish, Use a ladle to stir the water in the pan, to create a vortex, then slide the egg off the dish into the centre of the swirling water. Continue to swirl the water, taking care to not break the egg. The swirling water will (or should) help the egg stay compact, rather than spreading out as it would if the water were still. Lower the heat so the water is simmering, then continue to cook the egg for about three minutes, or until the white is softly set and the yolk is still runny. Use a slotted ladle to lift the egg from the water. Rinse it briefly under hot water (to remove the taste of vinegar) then lay the egg on paper towels, to blot up excess moisture. Cook the eggs one at a time.
Cut the spring onions lengthwise into long strips, then slice them into 3cm (1¼in) lengths. Put the pieces in a small pan and add the oil (or lard). Place the pan over a medium flame and cook until the spring onion sizzles and starts to brown. Remove from the heat.
Bring a pot of water to the boil and cook the shrimp roe noodles until done. Drain, rinse with cold water and drain again. Add about 10ml (2tsp) of the spring onion oil (or lard) and some of the sizzled spring onions and mix thoroughly. Put the noodles in a bowl and add a large dollop of XO sauce. If you like, sprinkle with dried shrimp roe.
If you made onsen eggs, crack an egg, put it in a bowl of ice water for a few minutes, then remove the shell. If you made poached eggs, remove one of them from the paper towels. Place the egg over the noodles and XO sauce, then combine thoroughly before eating. Any eggs that you don't use that day should be stored in the fridge. When you want to use one, warm the egg by covering it with hot tap water and leave for five minutes before proceeding.