Cut each chicken breast in half lengthwise. Place chicken between 2 sheets of heavy-duty plastic wrap; flatten to 1/4-inch thickness, using a rolling pin or flat side of a meat mallet. Sprinkle chicken with salt and pepper. Lightly dredge chicken in flour, shaking off excess.
Melt 1 Tbsp. butter with 1 Tbsp. olive oil in a large nonstick skillet over medium-high heat. Cook half of chicken in skillet 2 to 3 minutes on each side or until golden brown and done. Transfer chicken to a serving platter, and keep warm. Repeat procedure with 1 Tbsp. butter and remaining olive oil and chicken.
Add broth and lemon juice to skillet, and cook 1 to 2 minutes or until sauce is slightly thickened, stirring to loosen particles from bottom of skillet. Add 8 lemon slices.
Remove skillet from heat; add parsley and remaining 2 Tbsp. butter, and stir until butter melts. Pour sauce over chicken. Serve immediately. Garnish, if desired.