Gather Ingredients and Prepare Slow Cooker: Gather and prep all the ingredients. For easy clean up, line your crock pot with a slow cooker bag or liner; alternatively, lightly spray the bowl with non-stick cooking spray.
Season Steaks: Place the steaks on a clean work surface and pat dry with paper towels. Then, season the steaks generously on both sides with kosher salt and ground black pepper.
Layer Ingredients in the Slow Cooker: Scatter the sliced onions all over the bottom of the slow cooker. Next, pour in the broth and Worcestershire sauce. Then, place the seasoned steaks on top of the sliced onions. And sprinkle the top of the steaks with the French onion soup mix and minced garlic. Finally, lay the pats of butter, along with the fresh thyme sprigs if using, on top of the steaks.
Slow Cook Steaks: Cover the slow cooker and cook on low for 5½ - 7½ hours, or until the steak is cooked to your liking.
Rest: Transfer the steak and onions from the slow cooker to a platter or clean work surface and lightly tent with foil. Let the steaks rest for 5 minutes.
Serve and Enjoy: Serve slow cooked steaks with your favorite steakhouse side dish, such as warm dinner rolls, mashed potatoes, French fries and/or creamed spinach. Enjoy!