This is based on a recipe I saw in Chatelaine magazine. It is hands-down the best slow cooker recipe EVER! It's great served over mashed potatoes, but my favourite way to serve it is in kaiser buns, with the yummy shredded beef piled high on top. I put out toppings like arugula or lettuce, horseradish, mayonnaise, and sliced dill pickles, and let people fix their own bun the way they like it. Make sure to drizzle some of the wonderful sauce on each bun too, and also some of the onions too. Sooooo good!