Well, it's a basic beef stew flavored with curry, that is what Japanese curry rice should be in my mind... I do it in two parts. There is probably a more efficient way to do this, but I like a certain texture - it should be silken but also have a slight airiness and sweetness and a bit of vegetable texture to the gravy.
So you take some cubed stew beef (they can be huge cubes too, almost steak-like if you want), say a half kilo and season and dredge it, brown it well on all sides in oil, set that aside;
caramelize a whole diced brown onion and then a few diced carrots. Take the beef and the browned veggies and put in in a larger stockpot, and add a bottle of red wine, and then an equal amount of some sort of beef stock (I use veal stock, but beef stock is ok, even consomme would work) and then a can of tomatoes (the double size can, 28oz) and a bouquet garni - simmer gently for a good while, maybe 2-3 hours. Make sure it doesn't boil, otherwise your stock turns grey. This pot shouldn't thicken too much, but a little is good. You can add a bit of water here and there too if the level gets low and it tastes too strong. Skim the fat globules that rise to the top.
On the side while your beef simmers on slow, you should caramelize an absolute fuckload of onions, like 4-5, maybe 6 if you're crazy or your onions aren't too sweet, til they're soup brown, in oil. Add a finely diced apple and a finely diced banana at this point. Add a couple inch-long knob of ginger grated (or at least minced), and 3-4 cloves of garlic, minced. Saute those all together so that the onions are browned and everything else is at least softened. You should have something brown and soupy looking at this point. The browner, the better, scrape at the bottom of the pan if you need to.
Now you spice this onion mixture: basically, throw a fuckton of curry-related spices at it. Curry powder as a base, then maybe a tiny bit of garam masala (I don't like too much garam masala though, it's very strong on the cinnamon), some ground mustard, some ground cumin, a touch of ground coriander, ground cardomom, and then you can modulate the heat levels using four spices: white pepper, cayenne pepper, chili powder, and then some Japanese shichimi tougarashi. Start with a teaspoon of everything and then adjust to your liking.
Once you have your onions and stuff browned, and then spiced, hit it up with an immersion blender so that it's pasty, doesn't need to be 100% smooth. A bit of texture is good here.
So your original pot with the beef and wine and stock should be getting pretty good; use a spider and fish out the beef for a moment and set aside. It should still be brown but lost it's brown crust to the stock. Then, fish out the spent vegetables from the wine/stock base and the bouquet garni. You don't need those anymore. Alternatively, you can fish out the beef and then the bouquet garni, and then hit the rest with the blender.
Once that is done, put everything together, and simmer just a bit more while you prepare the last steps. Keep adjusting spices, as they die in intensity while they cook.
Get some pre-made demiglace base, maybe a small can, and add to the pot. The demiglace should thicken the soup pretty noticeably. Add some ground turmeric. You should be standing over a pot that smells and looks like a curry by this point, with a smooth sauce.
Taste and adjust the spices one last time if necessary, and then take a bitter dark chocolate bar and grate a little bit into the curry, stir it around. The curry is ready by this point. You can serve it this way with rice, or prepare some steamed vegetables on the side and arrange when you're lading up the curry - maybe a mix of things like carrots, potatoes, turnips, asparagus, broccoli, okra, cherry tomatoes. A soft-boiled egg is also a decent topping.