It took me a long time to learn this, but consistently (sometimes frustratingly) low heat and a long, long simmering time are key to tender braised beef. Something magical happens after the second hour, I swear. If you’re in a rush, this is fine for serving after one hour, but it’s incomparably good at two or three and only gets better with time. It also keeps wonderfully in the fridge for at least three to four days (plus the flavor will improve overnight) and will freeze for up to 3 months.
Many recipes call for parboiling the beef to remove impurities and adding the braising broth later — I didn’t see a huge difference in taste or quality by doing it all at once, so I omitted that step for simplicity’s sake.
Don’t worry if the stew seems like it’s taking forever to heat up or boil. The less it simmers, the better. If you want to shave a few minutes off the cooking time, you can start by heating it over medium heat for a few minutes, just until the liquid is almost hot but not boiling, then reduce to low heat.
Korean gochu peppers are generally milder and sweeter than jalapenos. If you can’t find them, Anaheim peppers would be a similar substitute; Italian long hot green peppers also work well. Alternatively, you could just use less jalapenos, one sliced and one or two whole. In addition, since it’s hard to tell sometimes how spicy peppers will be, I generally start conservatively and add a few more slices of jalapeno or a few more peppers about halfway through cooking if it’s too mild.
On that note, I find that these stews tend to vary in how much seasoning they need each time I make them, so in any case, it might be a good idea to taste the braising liquid (not the beef) about an hour in, or when the meat is fully cooked but still tough. If bland, add more soy sauce and pepper; if too spicy, add a bit of sugar and remove peppers; if too salty, remove some broth and add water.
Some versions of jangjorim add garlic or kombu for more flavor; you can do that if you like! Finally, you can also add a few eggs near the end, which soak up the stew flavor really nicely. To cook the eggs, add them (unshelled) to the pot about 15-20 minutes before the stew is done. Let simmer for 10 minutes, then remove and tap the shells with a knife or spoon to create cracks (like this post) and return to the broth until ready to serve.