Salt and pepper the brisket and brown on medium-high heat in a heavyweight Dutch oven. (You can also use an Instant Pot or pressure cooker.)
Remove the brisket and set aside.
Add the onions, garlic, and serrano peppers to the pot. Sauté until the onions and garlic are fragrant, about 4 to 5 minutes.
Add the beer to the pot and deglaze the pan. (Scrape of any crunchy bits and get them back into the sauce; there's a lot of flavor in there.)
Add the brisket back to the pot and cover it with the beef broth.
Add the spices and bring the liquid to a boil.
Cover and reduce the temperature to a simmer.
Cook for 2 hours.
The meat should be shreddable and falling apart when it's done.
RECIPE TIPS
Instant Pot Instructions: Brown the seasoned chuck roast. Add the onions and the broth. Cook on high pressure, "Manual," for 70 minutes. Let the pressure release for 10-15 minutes. Remove roast and place on a cutting board. Use 2 forks to shred. Dutch Oven Instructions: On the stovetop, brown the seasoned roast on all sides. Preheat the oven to 450℉. Place the roast in the oven and add the onions and the broth. Cover and cook for 30 minutes. Reduce temperature to 350℉ and then cook for an additional 3-4 hours. Slow Cooker Directions: After seasoning the chuck roast, brown on all sides. Add the onions to the slow cooker; add the roast, then the broth. Cook on low for 6 to 8 hours or on high for 4 to 5 hours.