Combine Worcestershire, ketchup, honey, oyster sauce, garlic powder, and whole grain mustard in a small pot over medium heat.
Simmer for 1–2 minutes until slightly thickened, remove from heat and cool.
Dry the wagyu, salt it, and let it sit for 30 minutes.
Coat the wagyu in flour, then egg, then panko, pressing the panko in.
Heat wagyu tallow to 180°C.
Deep fry the cutlet for 2 minutes until golden brown.
Season with flaky salt immediately, then rest for 10–15 minutes.
Toast milk bread on both sides in tallow over medium-low heat.
Melt smoked cheddar under one slice of bread as it toasts.
Add truffle aioli, tonkatsu sauce, and caramelised onions to the bread.
Place the wagyu cutlet on top.
Close the sandwich.
Trim the edges and cut into quarters.
