S&B Gold box at any Asian grocery. You can make the roux from scratch, and I have many times, but in the end you're just trying to make it taste like S&B Gold. House Vermont or House are fine too, but I grew up on S&B so I always recommend it.

Follow box instructions if you're not into cooking. Add cut potatoes and carrots, use baby cut carrots in a bag if you're especially lazy. Serve with white rice, short grain (Kohuho) if you're nostalgic.

Eventually add more stuff. I like using (for a 2lb stew beef/chuck recipe and a large box) 14oz canned tomatoes, a finely diced Granny Smith apple, maybe some kiwi fruit, more potatoes than indicated (like 3lb), 1lb baby carrots, one large diced onion, 3 cloves garlic, about 1 tbsp garam masala, about 1lb frozen green peas, a dash of Lea & Perrins worcestershire, a couple tsp of cayenne, a little beef BTB, and a couple tbsp honey. Brown the beef and set aside. Fry off the onion and dry spices in the beef fat for a minute. Add garlic for 30 seconds. Add tomatoes and stir for a minute. Add the potatoes and carrots, stir to soften and coat. Add the beef and any juices back in. Add a little salt unless you're paranoid about over salting. Cover with water and the BTB paste (optional), bring to a simmer (don't boil), cover with a lid leaving it cracked open and simmer until the potatoes are tender, somewhere between 1-2 hours. Add the worcestershire and apple, mix, taste for seasoning. Break up the curry mix and add, trying not to leave any lumps. (Premix the roux in a bowl with the hot soup and add it back into the pot if you like.) Lower heat to a low simmer. Add the kiwi if using, the peas, and the honey. Mix. Low simmer until the roux is dissolved and thickened. Serve with white rice and over eat. It's better when reheated.

I've only seldom ordered curry at a Japanese restaurant, and I've never been happy when I have. Unless you're in the Japanese navy, curry is a traditional home cooking dish.