Napa cabbage and thinly sliced sour pickles add texture and tang to this hearty stew. Searing the pieces of beef chuck before putting them in the slow cooker gives the stew a rich flavor.
In a very large skillet, heat the oil. Season the meat with salt and pepper and sear the pieces over moderately high heat until richly browned all over. Transfer the meat to a large slow cooker, turn it to high and cover.
Wipe out the skillet and return it to the burner. Add the soy sauce, sugar, wine and stock and bring to a boil. Pour the mixture into the slow cooker. Add the onions, cover and cook for 2 hours. Add the garlic and jalapeños to the stew, cover and cook for 1 hour longer, until the meat is very tender.
Meanwhile, bring a medium saucepan of water to a boil. Add the bean sprouts and blanch for 30 seconds; drain. Put the cornstarch in a bowl and whisk in 1/2 cup of the liquid from the cooker.
With a slotted spoon, pick out and discard the onions. Transfer the meat to a large bowl. Whisk the cornstarch mixture, then whisk it into the stew, cover and let simmer for 2 minutes. With 2 forks, very coarsely shred the meat. Return the meat to the cooker. Add the Napa cabbage and pickles to the cooker, cover and cook until the cabbage is just wilted, about 5 minutes. Turn the cooker off.
Spoon steamed rice into bowls. Ladle the stew over and around the rice. Top with the beans sprouts, a drizzle of sesame oil and the sliced scallions and serve.