Reserve 1/2 cup of the chocolate chips for glaze; place remaining chips in medium microwavable bowl (or place in top of double boiler). Stir in yogurt until chips are coated. Microwave on High in 1-minute increments, stirring after each, until chips are completely melted (or heat in double boiler over simmering water, stirring frequently, until melted). Stir in crushed granola bars and egg whites until well blended. Pour batter into pan.