Low and slow is the only way with brisket. By Sunday dinner, the meat practically melts, and those roasted carrots turn sweet and tender alongside it.
Preheat your oven to 300°F and set a large Dutch oven over medium-high heat. Pat the brisket dry and season generously on all sides with kosher salt and black pepper.
Add olive oil to the pot. When hot, sear the brisket for 3–4 minutes per side until deeply browned, then transfer to a plate.
Add sliced onions and celery to the same pot, sautéing over medium heat for 4–5 minutes until softened. Stir in minced garlic and dried thyme; cook for 1 minute until fragrant.
Return the brisket to the pot. Pour in beef broth and nestle whole peeled carrots around the meat. Bring to a simmer, cover tightly, and transfer to the oven.
Roast for 3.5–4 hours, basting the brisket halfway through and turning carrots if needed for even cooking. The brisket is done when tender enough to shred with a fork.
Let the brisket rest uncovered for 10 minutes before slicing across the grain. Serve the brisket with roasted carrots and spoon pan juices over the top.