In a large Dutch oven, heat the olive oil over medium-high heat. Season the short ribs with salt and pepper, then sear them in the hot oil until browned on all sides, about 3-4 minutes per side. Remove the ribs and set aside.
In the same pot, add the chopped onion and cook until softened, about 5 minutes. Stir in the minced garlic and cook for an additional minute until fragrant.
Pour in the beer, scraping up any browned bits from the bottom of the pot. Add the beef broth, Dijon mustard, brown sugar, thyme, and return the short ribs to the pot.
Bring the mixture to a simmer, then cover the pot and transfer it to the preheated oven. Braise for 2.5 to 3 hours, or until the meat is tender and easily pulls away from the bone.
Once done, remove the pot from the oven and let it rest for 10 minutes. Skim off any excess fat from the surface before serving.
Serve the short ribs with the sauce spooned over the top and garnish with fresh parsley.
Notes
For a richer flavor, add a tablespoon of Worcestershire sauce to the braising liquid.
Serve with mashed potatoes or crusty bread to soak up the delicious sauce.