Sear the base. Pat the beef dry. In a heavy saucepan, combine beef, onion, and 1 cup water. Bring to a boil, then reduce to a simmer, covered, for 30 minutes.
Concentrate the flavour. Uncover, raise heat to high, and cook — stirring often — until the liquid evaporates and the beef and onions turn lightly golden, 5–7 minutes. Lift the meat out and set aside.
Bloom the spices. In the same pan, add the curry powder, mustard seeds, garlic, and turmeric. Toast for about a minute, stirring constantly, until fragrant.
Build and braise. Pour in the broth, then add the tomatoes, jalapeños, and ginger, scraping up any browned bits from the base of the pan. Return the beef, bring to a boil, then cover and simmer gently for 2–2½ hours (or 30 minutes in a pressure cooker) until the beef is fork-tender. Season with salt to taste.