Combine miso and soy in a small bowl. Stir to combine thoroughly.
Mix the miso mixture with the beef and refrigerate 4 to 12 hours.
Pre-heat your oven to 325F.
Film a pot generously with vegetable oil. Brown the beef in batches over medium low heat. Leave room around the beef. You don't want it to steam. You want it brown. Take your time. Every stove is different. You may need to adjust the heat. Do what works for you.
Transfer the browned beef to a clean dutch oven. Add the garlic and the gochugaru to the pot.
Make your dashi. Bring the hon-dashi and water to a boil. Let simmer briefly.
Mix the gochujang with a couple tablespoons of hot dashi in a small bowl. Add a bit more dashi if needed. Get the gochujang to dissolve in the dashi. It's way easier to do this in a small bowl. Chasing miso or gochujang around a large pot is a pain.
Add the gochujang mixture. Now add enough of the remaining dashi to come up 2/3 of the way up the meat.
Cover the dutch oven with aluminum foil or parchment. Then put the lid on it.
Place in the oven and braise for about an hour. After an hour give it a stir and return it to the oven.
Beef is done when it is tender. This will take probably around 3 to 3 1/2 hours if you have big chunks. Start checking after 2 1/2 hours. There's no way to rush this. It's ready when it's ready.
It reheats well though so just plan ahead. Give yourself some extra time. Reheat to serve. Much better than having your guests wait an extra hour or two for dinner...