In a large skillet over medium-high heat, melt 1 tablespoon butter. Add mushrooms, lemon zest, and lemon juice. Cover and simmer 5 minutes. Uncover and add garlic (optional), cook over high heat until liquid almost evaporates and mushrooms brown and glaze, about 5 minutes. Add white wine, 1/4 cup broth. Stir to scrape up browned bits in pan. Pour into a small bowl.
Sprinkle both sides of chicken thighs with salt, pepper and flour. Add 2 tablespoons of butter to skillet and melt over medium high heat. Add chicken to pan and cook until lightly browned, 4 minutes. Turn over and cook for another 6 minutes. Remove to platter, cover to keep warm.
Pour cooked mushrooms back into pan and add remaining 1/4 cup chicken broth, 1/4 cup parsley, scraping to release brown bits on bottom of pan. Add remaining 1 tablespoon butter and swirl in pan until melted. Drain juice from cooked chicken into pan. Pour mushroom sauce over chicken, sprinkle with remaining parsley and serve.
Video
Notes
1. I use 4 boneless and skinless chicken thighs weighed in about 1 1/2 pounds total. Pound meat with a flat-surface mallet until about 1/4 in. thick.