Pat the chicken thighs dry with a paper towel and place into a large bowl. Season with kosher salt, black pepper, onion powder, garlic powder, and poultry seasoning.
Drizzle olive oil into a 12-inch nonstick skillet over medium high heat. Place the chicken thighs into the pan and sear on both sides for 5 minutes per side, until golden brown. Remove the chicken from pan and place into the bottom of the slow cooker.
Reduce heat to low. Add condensed french onion soup, Worcestershire sauce, and beef broth into the pan to deglaze the pan. Use a wooden spoon or rubber spatula to scrape the bits off of the bottom of the pan, then pour into the crockpot.
Add sliced onions on top of the chicken in the slow cooker, then sprinkle french onion soup mix on top.
Add diced garlic, bay leaves, and thyme, ensuring it's submerged in the liquid. Place sliced butter on top. Cover with the lid and cook on low heat for 6 hours, until the chicken is tender and falls off of the bone. (you can also cook on high heat for 4 hours, but I recommend low heat for best results)
Remove the chicken along with the juices and onions and add back into a casserole dish or large oven safe skillet Coat with shredded gruyere cheese and broil in the oven for 3-5 minutes, until the cheese melts and becomes golden brown. (You can also add the cheese to the crockpot and continue to cook for an additional hour) Serve with crusty bread and mashed potatoes or white rice for the ultimate comfort meal.
Notes
Cook Low and Slow: For the most tender, flavorful chicken, cook on the low setting for 6-8 hours. While the high setting is faster, the low setting allows the flavors to fully develop and ensures the chicken stays moist.
Choose the Right Chicken: Boneless, skinless chicken breasts or bone-in thighs work best for this recipe. Thighs are less likely to dry out, but if you prefer breasts, keep an eye on cooking time to avoid overcooking. For added flavor, sear the chicken before placing it in the crock pot.
For thicker gravy, omit the beef broth. If you like the extra gravy, make a cornstarch slurry by combining 1-2 tablespoons cornstarch and 2 tbsp water to a small bowl. Mix together and add to the broth halfway through the cooking process, stir, and continue cooking.
Ensure the fresh herbs are the submerged in the broth - the heat is what extracts the flavors.