Optional step: Add 50 ml chicken stock and ½ tsp gelatin powder to a microwaveable bowl. Let it bloom for 5-10 minutes and then microwave for 20-second intervals until the gelatin has dissolved. Place it in the refrigerator to set (approx 3 hours). Once set, use a spoon to mix and break it up into small pieces.
Heat a frying pan on medium and melt 1 tsp butter. Add 100 g onion and fry until softened and slightly golden.
Add 100 g ground beef to the pan and fry until browned.
Pour in ½ tbsp mirin and 1 tbsp Worcestershire sauce. Stir and continue to fry until the liquid is almost gone, then remove the pan from heat and leave the mixture to cool to room temperature.
In a small bowl, mix 3 tbsp panko breadcrumbs with 1 ½ tbsp whole milk.
Place 150 g ground beef in a mixing bowl and sprinkle with 1 pinch salt and pepper.
Add the wet panko mixture, 1 egg yolk, ½ tsp tomato ketchup, 1 tsp sugar, 1 pinch nutmeg powder, and the cooled meat/onion mixture from earlier to the bowl. Mix well. (If using chicken stock jelly, add that here too.)
Divide the mixture into equal portions (I shaped into 4) and shape into ovals/discs.
Place the patties on a tray, cover and rest in the fridge for 30 minutes.
Preheat your oil to 160 °C (320 °F). While you wait, prepare 3 plates or containers. One with 85 g all-purpose flour, one with 1 egg (whisked) and one with 150 g panko breadcrumbs.
Coat each patty with flour and pat off the excess. Coat with an even layer of whisked egg and then a generous layer of panko breadcrumbs. Press them down gently without squashing the patty to secure them.
Coat each patty with egg and panko one more time.
Place the breaded patties in the oil and fry for 2 minutes on each side. Be careful not to overcrowd the oil and cook in batches if necessary.
Remove the patties from the oil and place them on a wire rack. Increase the heat of the oil to 180 °C (356 °F).
Once the oil temperature has increased, return the menchi katsu to the oil for 1-2 minutes on each side or until golden and crispy.
Place on a wire rack to drain the excess oil.
Mix the sauce ingredients in a small bowl or serving jug.
Serve menchi katsu with a sprinkling of dry parsley and the homemade sauce. Drizzle or dip and enjoy!
Notes
Cooking time doesn't include chicken jelly because it's an optional step.Adding chicken jelly makes the patty juicier and more flavourful, but takes longer and can be harder to shape.