Pat the roast dry with paper towels. Mix salt, pepper, garlic powder, and onion powder in a small bowl. Rub the blend all over the roast, pressing it into the meat.

Heat the oil in a large skillet over medium-high heat until shimmering. Sear the roast 3–4 minutes per side until nicely browned. Don’t skip this — browning builds flavor.

Arrange the sliced onion across the bottom of the slow cooker. Scatter carrots, potatoes, and celery over the onions if using.

Place the seared roast on top of the onions and vegetables in the slow cooker.

Whisk together beef broth, Worcestershire sauce, soy sauce (if using), minced garlic, thyme, and bay leaves. Pour the mixture around and over the roast.

Cover and cook on LOW for 8–10 hours or on HIGH for 4–5 hours. The roast is done when a fork slides into the meat easily and it’s very tender.

Carefully lift the meat onto a large platter. Use a slotted spoon to remove vegetables and arrange them around the meat.

Strain the cooking liquid into a bowl and measure out about 3 cups for making the gravy. Discard solids and bay leaves.

In a medium saucepan, melt the butter over medium heat. Whisk in the flour to form a roux and cook until bubbly and lightly golden, about 1–2 minutes.

Slowly whisk the hot reserved cooking liquid into the roux, a little at a time to prevent lumps. Simmer until the gravy thickens and coats the back of a spoon.

Taste and adjust seasoning with salt and pepper.

Slice or shred the roast and spoon gravy over the meat and vegetables. Serve immediately.