Peel potatoes and cut into fairly large chunks. Place potatoes in the bottom of the slow cooker.
In a medium bowl, combine coriander, brown sugar, ginger, curry paste, fish sauce, Worcestershire sauce, coconut milk, tapioca, and water. Whisk until it is smooth. Pour over the potatoes in the slow cooker.
Cut beef into bite-size cubes and place cubed beef in the slow cooker. Press to submerge in the liquid.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until potatoes are soft and beef is tender.
Stir in the lime juice and peanut butter. Top with peanuts and cilantro, if desired and serve over rice.