Prep: Pound chicken to 1/4-inch thickness. Mix flour, garlic powder, salt, and pepper. Dredge chicken and shake off excess.
Sear: Heat oil and 1 tbsp butter in a large skillet. Sear chicken until golden (3-4 mins per side). Remove and set aside.
Sauté: Add remaining butter to the pan. Sauté mushrooms and shallots until browned (approx. 6 mins). Add garlic for the final minute.
Deglaze: Pour in broth and vinegar. Scape the pan bits. Simmer for 5 mins until reduced by half.
Cream: Stir in heavy cream. Simmer until the sauce thickens slightly.
Finish: Return chicken to the pan. Spoon sauce over. Simmer 2 mins. Garnish with parsley and serve.