Preheat oven to 325°F (163°C).
Pat the beef roast dry and season all surfaces thoroughly with salt and pepper.
Heat vegetable oil in a heavy-bottomed Dutch oven over medium-high heat until shimmering.
Sear the beef for 4-5 minutes per side until a deep brown crust (Maillard reaction) has developed; remove and set aside.
Reduce heat to medium, add sliced onions to the rendered fat, and sauté until golden brown and softened, approximately 10-12 minutes.
Add minced garlic and cook for 60 seconds until fragrant.
Deglaze the pot with hard apple cider, scraping the bottom to incorporate the fond.
Add beef stock, apple cider vinegar, thyme sprigs, and bay leaves.
Return the beef to the pot, bring the liquid to a simmer, then cover with a tight-fitting lid.
Transfer to the oven and braise for 2 hours and 30 minutes.
Incorporate carrots into the braising liquid around the beef and continue cooking for 60 minutes or until the beef is fork-tender.
Remove the beef and carrots to a serving platter; discard the thyme stems and bay leaves.
Optional: Reduce the remaining braising liquid over medium-high heat for 5-8 minutes to thicken into a sauce before serving.