Pound chicken (or veal) until thin. Dredge lightly on both sides with flour. In large skillet, melt 2 Tbsp. butter and saute mushrooms over medium heat until browned, about 10 minutes. Remove mushrooms and set aside.
Melt remaining 2 Tbsp. butter in skillet. Add chicken and cook through, 4 minutes on each side. Remove to serving platter. Return mushrooms to pan, stir in cooking wine, water, parsley and rosemary. Heat and pour over chicken.