Add the sliced white onion to the bottom of the slow cooker. Add the chuck roast on top.
Add the garlic cloves on top of the roast. Pour over the French onion soup and beer.
Cover and cook on low for 10 hours without opening the lid during the cooking time.
When the cooking time is done, remove the roast on to plate. Shred the meat with 2 forks.
I like to remove the grease from the drippings in the slow cooker. I do this by laying paper towels over the top and quickly remove. Discard paper towels.
To serve, I like to toast the buns in the oven under the broiler, then add the meat and cheese and put back in the oven until the cheese melts. Don't forget the sandwiches in the oven, they will burn very quickly under the broiler. Serve the sandwiches with the drippings (au jus) in the slow cooker.
Nutritional values are approximate. If you require a special diet, please use your own calculations. Value below are for 1/8 of recipe (beef and au jus). It does not include rolls or cheese.