In a small bowl, mix the minced garlic, onion powder, garlic powder, salt and pepper together. Pat the meat dry with paper towels, then rub the blend over the entire outside of the roast.
Place the wine and the beef broth in the slow cooker and stir in the tomato paste until fairly well blended. Place the roast in the slow cooker, fattier side up, and add the chopped onion on top. Cook on low for 10 hours until the meat is fall apart tender. Remove from the slow cooker and let sit for 15 minutes.
Slice (it will fall apart as you do — that’s a good thing!) and place on a serving platter. Spoon some of the cooking juices with the cooked onion over the top.
Notes
You don’t have to add much liquid to the slow cooker when you are cooking a roast, but in this case there is 1 cup of wine and 1 cup of beef broth, which provides lots of flavorful cooking juices to drizzle over the meat after it has rested and been sliced. The larger amount of liquid also gives you the ability to let the roast stay moist and tender in the slow cooker for a bit longer (see below), and not get overcooked or tough.The roast itself will release some liquid, so if you want less cooking juices at the end, you can reduce the amount of the wine and the broth to ½ cup each. You can also use all broth if you prefer. I often use a mixture of wine and broth when cooking, making sauces and such because I like the way the flavors of each build upon each other.