To cook a beef joint in a slow cooker, the key steps are seasoning and optionally searing the beef, then cooking it low and slow with vegetables and liquid for several hours until tender. Here is a summarized method:

1. Season the beef joint (topside or shoulder) with salt, pepper, flour, and herbs like thyme and garlic powder.
2. Optionally brown the beef in a hot pan with oil to seal in flavor.
3. Place chopped vegetables such as onions, carrots, and garlic in the slow cooker base.
4. Add the beef joint on top of the vegetables.
5. Pour in beef stock or broth (and optionally some wine or Worcestershire sauce) to partially cover the meat.
6. Cook on LOW for about 7-8 hours or on HIGH for 5-6 hours until the beef is tender and reaches an internal temperature between 195-200°F for tender, fall-apart texture.
7. Once cooked, remove the beef and vegetables.
8. To make gravy, thicken the cooking juices with a cornstarch slurry by cooking it on the stove or back in the slow cooker on high for about 30 minutes, whisking to avoid lumps.
9. Rest the beef before slicing and serve with the vegetables and thickened gravy.

This approach fits many slow cooker beef joint recipes and delivers tender, flavorful meat with rich gravy and cooked vegetables. Topside is a good choice for the joint. The whole process is low-effort with maximum cooking convenience and delicious results.

If needed, I can provide a detailed recipe with exact ingredient amounts and timing.