Season the meat with 1 teaspoon kosher salt and ¼ teaspoon black pepper.
Place the roast in the slow cooker pan and add the sliced onion, garlic, and parsley. Pour the beef broth (or wine) on top.
Cover and cook on LOW for 7 hours.
Remove the meat to a plate. Set the slow cooker to WARM. Strain the cooking liquids into a glass measuring cup, then return the meat to the slow cooker and cover it to keep warm while you make the gravy.
Use a spoon to skim the fat layer off the top of the cooking liquids. Season them with ½ teaspoon kosher salt and ¼ teaspoon black pepper. Transfer to a medium saucepan. Heat over medium heat, and continue to simmer, whisking occasionally, until reduced into a rich sauce, about 10 minutes.
Flake the beef with a fork. Distribute evenly among plates lined with mashed cauliflower. Spoon 2-4 tablespoons of gravy on top of each plate and serve.
Video
Notes
Nutrition info source: University of Rochester Medical Center. While ideally, you would brown the meat on the stovetop before placing it into the slow cooker, this is not strictly necessary. I've experimented and found that it makes little difference to the final outcome, so I skip this annoying step. Although it won't hurt to do it if you have the patience.