Pat the beef roast dry with paper towels and season it generously with salt, pepper, and thyme.

Heat the olive oil in a large skillet over medium-high heat until shimmering, then carefully add the beef.

Sear the meat on all sides until it develops a deep golden-brown crust, about 4-5 minutes per side, then transfer it to the slow cooker.

Add sliced onions, carrots, and chopped celery to the skillet and cook until the onions start to soften and become fragrant, about 5 minutes.

Stir in the minced garlic and cook for another minute until fragrant, then pour the vegetable mixture over the beef in the slow cooker.

Pour in the beef broth around the meat and vegetables, ensuring the liquid covers about half of the roast.

Cover the slow cooker with the lid and cook on low for 8 hours, until the beef is fork-tender and easily pulls apart.

Remove the beef from the slow cooker and transfer it to a platter. Tent it loosely with foil to keep warm.

Strain the cooking liquid into a saucepan, discarding the solids, then bring it to a simmer over medium heat.

Whisk the flour into a small amount of cold water to create a slurry, then slowly stir it into the simmering liquid to thicken into a gravy.

Cook the gravy for about 3-5 minutes until it thickens and coats the back of a spoon, then pour it over the sliced beef or serve on the side.

Slice or pull apart the tender beef, serve with vegetables and gravy, and enjoy the hearty, melt-in-your-mouth texture.