Meanwhile, in 2-quart heavy saucepan, melt butter over medium heat. Stir in condensed milk, brown sugar and granulated sugar until blended. Add graham cracker crumbs; mix well (mixture will be thick). Bring to a boil, stirring constantly. Reduce heat to low; cook 5 minutes, stirring constantly, or until slightly thickened. Pour caramel mixture over warm cookie crust, spreading evenly.