Preheat your oven to 325°F (163°C).
In a large Dutch oven, heat the olive oil over medium-high heat. Season the short ribs with salt and pepper, then brown them on all sides in the hot oil. Remove the ribs and set them aside.
In the same pot, add the chopped onion and cook until softened, about 5 minutes. Add the minced garlic and cook for an additional minute until fragrant.
Pour in the beer, scraping the bottom of the pot to deglaze and lift any browned bits. Stir in the beef broth, Dijon mustard, brown sugar, thyme, and bay leaf.
Return the short ribs to the pot, ensuring they are submerged in the liquid. Bring the mixture to a simmer.
Cover the pot and transfer it to the preheated oven. Braise for 2.5 to 3 hours, or until the meat is tender and falling off 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 of the sauce.
Serve the short ribs with the sauce spooned over the top, garnished with fresh parsley if desired.