First, I pick my roast with some marbling for moisture. I heat a skillet high, add a little oil, and sear the roast about 2 minutes per side to lock in flavor.
Then I place the seared roast in the slow cooker. I add the chopped onion, chipotle chilies (or jalapeños), chili powder, cumin, salt, pepper, and pour in beef broth so the meat is partly submerged.
I set the cooker to low for about 8 hours (or high for ~5 hours) and let the roast cook until it’s fall-apart tender. When it is, I use two forks to shred the beef.
After shredding, I taste and adjust salt or chili powder if needed. Letting it sit in its juices really helps unify the flavors.