Combine the balsamic vinegar, soy sauce, brown sugar, minced garlic, and dried thyme in a small bowl. Stir until well combined and set aside.

Pat the chicken thighs dry and season both sides lightly with salt and black pepper.

Heat a large skillet over medium heat. Add the olive oil and swirl it around the skillet to coat the surface.

Add the chicken thighs and cook until deeply browned and completely cooked through, about 7–8 minutes on the first side and 4–5 minutes on the second side. Chicken should reach an internal temperature of 165°F (74°C). Transfer it to a clean plate and loosely cover to keep warm.

Add the mushrooms to the same skillet. Cook for 5–7 minutes, stirring occasionally, until tender and nicely browned.

Reduce the heat to medium-low. Pour the prepared balsamic mixture over the mushrooms. Scrape the bottom of the skillet to loosen the flavorful browned bits.

Bring the sauce to a gentle simmer and cook for approximately 4–5 minutes, stirring occasionally, until it has reduced and becomes slightly syrupy.

Stir in the butter until completely melted and incorporated into the sauce.

Return the chicken thighs to the skillet. Turn them several times so they are generously coated in the sauce, then simmer for another 2–3 minutes. Your Balsamic Chicken and Mushrooms is ready when the chicken is hot and covered in the glossy balsamic sauce.

Serve immediately, spooning the mushrooms and extra pan sauce over each chicken thigh.