Cut chuck roast into 2" cubes. In large skillet, over medium heat, sauté meat in oil until well browned on all sides.
Remove meat to bowl and season with salt and pepper.
In same skillet, melt butter and sauté onion, stirring often, until medium brown.
A minute before onion is done, stir in garlic. Turn onion and garlic into crock pot. Add browned meat and juices from bowl.
To still-hot skillet, add beer, sugar, salt, parsley, bay leaf, and thyme. Scrape up pan juices and turn into crock pot.
Cover and cook on Low 8-10 hours.
Pour cooking liquid into measuring cup. If you have more than 2 cup liquid, cook in skillet, over high heat, until reduced.
Thicken sauce by simmering cornstarch dissolved in vinegar 3-4 minutes, stirring constantly.
Place onion in serving dish; set meat cubes on top, and spoon sauce over all.
Servings: 4 to 6