Cut the cabbage, onion, and carrot into similarly sized pieces.
In a separate pan, sear the beef over high heat, seasoning it with a pinch of salt as it cooks.
In a large pot, add the onion first and sauté over medium heat for about 5 minutes.
Add the cabbage, carrot, and the seared beef, then continue sautéing over medium heat for another 10 minutes. Adding a little salt at this stage also helps bring out the vegetables' natural sweetness.
Pour in just enough water to cover the ingredients, then add the chicken stock powder, ketchup, and tonkatsu sauce. Simmer for about 5 minutes.
Add all the curry roux and stir until fully dissolved, adding a bit more water only as needed to reach your desired seasoning.
Simmer over medium heat for about 15 minutes, stirring occasionally so it doesn't stick to the bottom, and it's done.
Tip.Curry actually tastes better after it cools down and gets reheated, since the flavors have time to meld together and deepen. I'd recommend making it a few hours ahead and reheating it before serving.