Cover the chicken breasts with plastic wrap and lightly pound them using a meat tenderizer or a rolling pin. Season with salt, pepper, and dried thyme.

In a large skillet, add 1 1/2 tbsp olive oil and cook seasoned chicken breasts on each side until brown or about 6-8 minutes on each side. Remove from the skillet and set aside. Wipe the skillet clean with a paper towel.

Add the butter and the remaining 1 1/2 tbsp olive oil to the same skillet.

Cook the onions on medium heat, stirring frequently until browned and softened. It takes about 20-25 minutes.

Then, add the minced garlic and cook until fragrant, about one more minute.

Add the flour and stir until combined. Then, pour in the beef broth and Worcestershire sauce. Stir together. Place the chicken back into the skillet. Top with a sprig of fresh thyme. Let simmer for 15-20 minutes until the sauce has thickened and the chicken is cooked through.

Place two mozzarella slices on top of each chicken breast. Cover with a lid and cook until melted. Enjoy!