Step 1

Pat the chuck roast down and season it with salt and pepper.

Step 2

Heat a large skillet over medium-high heat.

Step 3

Add the butter and the oil to the skillet.

Step 4

Once the butter has melted and starts to crackle, add the chuck roast and sear, about 2-3 minutes per side.

Step 5

Transfer the roast to a plate.

Step 6

Add 1/2 of the onions, the garlic, the beef broth, the Worcestershire sauce, the vinegar, the onion powder, the thyme, the bay leaf, the celery seeds, the sugar, and the seared chuck roast to a slow cooker.

Step 7

Top the roast with the remaining 1/2 of the onions.

Step 8

Cover and cook on low until the roast is fall-apart tender, about 6-8 hours.

Step 9

Transfer the meat to a plate, covering it to keep it warm.

Step 10

Combine the cornstarch and the water to create a slurry.

Step 11

Add the slurry to the slow cooker and stir.

Step 12

Allow the mixture in the slow cooker to cook until thickened, about 5-7 minutes. If the sauce still seems too thin, add additional cornstarch slurry, 1 tablespoon of cornstarch to every 2 tablespoons of water at a time, and cook for an additional 5 minutes.

Step 13

Remove and discard the bay leaf.

Step 14

Return the meat to the slow cooker and heat through. Serve.