Season the beef with salt and pepper. (Or my favorite, Montreal Steak Seasoning.)
Place in the slow cooker with onions, balsamic vinegar, tomato paste, bay leaves and tapioca, if using.
Cover and cook on Low until meltingly tender, 8 to 10 hours. (This will vary depending on the size of your slow cooker, size of beef, and how hot your slow cooker cooks.)
To cook in the oven instead, add in a cup of water, cover and bake at 250 degrees for 6-8 hours or until beef is meltingly tender. Add in a little water if the beef starts to dry out.
Taste, season with salt and pepper and serve hot with your chosen accompaniments.

Note:

Ideal Slow Cooker Size: 4-Quart.

Can add 1-2 tablespoons of instant granulated tapioca as an optional thickener.

* Weight Watchers Friendly