Add butter into a small frying pan over medium heat.
Add finely chopped onion and cook it until onion become transparent and soft.
Let it cool and set aside.
Place ground meat in a mixing bowl and add egg, salt, potato starch and cooked onion.
Combine them well with your hand until it become a little sticky. Make 18 pin-pong ball sized meatballs.
Heat oil to 180°C (356°F) and deep fry the meatballs until it become golden brown. *13
Set aside the meatballs. You could do up to this steps a night before in order to save time in the morning.
Place water, torigara soup powder, soy sauce, sugar, mirin, rice vinegar and potato starch in a saucepan.
Bring it simmer and become thicken.
Add meatballs to the saucepan and coat the thickened sauce well.
Crack the eggs into a mixing bowl and add shirodashi.
Mix them all together and strain the egg mixture a few times.
Heat the oil in a rectangle shaped frying pan(if you have)*14 and remove the excess with a kitchen paper. Keep the oil soaked kitchen paper for later steps.
Pour about 1/3 of egg mixture, scramble them a little bit and when the egg solidified a little, push them towards an end ot of the pan.
Wipe the empty side of the pan with oil soaked kitchen paper and pour another 1/3 of the egg mixture.
Lift the pushed egg to let the egg mixture run under it.
Place the nori sheet over the newly poured egg before they get solidified.
Roll the egg from the one side of the pan.
Repeat the same for remaining egg mixture.
Turn the heat off and remove the rolled egg from the pan and let it cool.
Slice the rolled egg about 2cm(7.9inch) thick.
Potato salad *9
Chop the onion finely and soak them in water in a small mixing bowl. Soak about 10 minutes. Drain the water and squeeze out excess water and set aside.
Slice the cucumber thinly and sprinkle a pinch of water. Leave it about 5 minutes or the salt withdraw the water out of cucumber. Squeeze the moisture out of cucumber and set aside.
Peel the potato and cut them small.
Boil the potato for about 10 minutes or potato become soft. Drain the cooking water and mash the potatoes.
Place mashed potato, onion, cucumber and ham into a mixing bowl.
Add mayonnaise and salt to combine them all together.
Assemble all together into a lunch box
Place rice first, then shiso leaves, meatballs, sugar snap peas, rolled egg, tomato and potato salad. If there is any gap, fill the gap with green vegetables and parsley.
Sprinkle sesame seeds over the rice and top with Umeboshi. *See above step by step photos.
*1 average Japanese 1 rice bowl serve about 150g of cooked rice.*2 makes about 18 meatballs. Use 4 for one Obento box. Also see Teriyaki Meatballs*3 I only had pork in my fridge, but it can be substituted with beef, veal, pork and beef etc.*4 for deep fry. You can bake or fry. 20ml of the oil absorbed and calculated into nutrition fact.*5 Torigara is marchandise name of chicken carcass soup powder. You can purchase Chicken Broth Powder *6 If you can not access to rice vinegar, you can substitute with white vinegar.*7 See also Tamagoyaki There is a video instruction if you are not sure of any steps.*8 Shirodashi is bottled liquid dashi.*9 See also Potato salad*10 If you can not access Kewpie Japanese Mayonnaise it can be substitute with any mayonnaise.*11 If you can not access to Shiso leave, omit it or use lettuce leaves instead.*12 half of the egg used for making meatballs and half of the egg used for egg roll.*13 alternatively you can fry them in frying pan if you don't like deep-fry.*14 if you don't have rectangle or square pan, just use round one, you can still roll the egg.*15 Nutrition fact is calculated based on all ingredients listed. However you don't pack everything. Actual energy of one packed Obento with above menu is approximately 542 cal.