1 cup sugar
¼ cup light corn syrup
2 T water
1½ t vingegar
¼ cup butter cut into 8 pieces
¼ t vanilla
Line an 8x8x2" baking pan with foil, extending foil over edges of pan. Butter the foil; set aside.
Butter the sides of a heavy 1 quart saucepan. In the saucepan combine sugar, light corn syrup, water and vinegar. Cook over medium heat to boiling., stirring constantly with a wooden spoon to dissolve sugar. This should take about 5 minutes. Carefully clip candy thermometer to side of pan.
Cook over medium heat, stirring constantly, while adding the ¼ cup butter, 2 pieces at a time. Continue cooking over medium heat, stirring occasionally, till thermometer registers 300°, hard crack stage. Mixture should boil at a moderate, steady rate over the entire surface. Reaching hard crack stage should take 25 to 30 minutes.
Remove saucepan from heat; remove thermometer from saucepan. Stir in vanilla. Pour mixture into prepared pan Let stand 5 to 10 minutes or till a film forms over surface of candy.
Using a broad spatula or pancake turner, begin marking candy by pressing a line across surface, ½" from edge of pan. Do not break the film on the surface. Repeat along other three sides of pan, intersecting lines at corners to form squares ( If candy does not hold it's shape, it is not cool enough to mark. Let candy stand a few more minutes and start again)
Continue marking lines along all sides, ½" apart, till you reach the center. Retrace previous lines, pressing the spatula deeper but not breaking film on surface. Repeat till the spatula can be pressed to the bottom of pan along all lines.
Cool completely. Use the foil to lift candy out of the pan; break into squares. Store tightly covered.
Makes about 2/3 pound