Start by trimming the fat cap on your brisket to about 1/4 inch thick to retain moisture while cooking.
Create a rub by combining brown sugar, kosher salt, and black pepper in a bowl.
Apply the onion soup mix and your rub generously on both sides of the brisket.
Place the brisket fat cap side down in your slow cooker.
Scatter minced garlic, sliced red onions, thyme, and bay leaves over and around the brisket.
In a mixing bowl, whisk together beef broth, soy sauce, Worcestershire sauce, lemon juice, and liquid smoke if using.
Pour this flavorful liquid over the brisket in the slow cooker.
Cook on low heat for 8-10 hours; remember, the longer it cooks, the more tender the beef becomes.