Line 15x10x1-inch baking pan with foil, extending foil over sides of pan; grease foil. In Dutch oven or 4-quart saucepan, combine sugar, butter and evaporated milk; cook over medium heat until sugar is dissolved, stirring frequently. Bring to a full boil, stirring constantly. Without stirring, boil 5 to 6 minutes over medium heat or until candy thermometer registers 234°F. Remove saucepan from heat.