Generously butter 2 cookies sheets. In large heavy saucepan, combine sugar, corn syrup, and water. Cook until sugar dissolves, stirring constantly. Continue cooking until candy thermometer reaches hard crack stage (300°F.), stirring occasionally. Remove from heat; stir in vanilla and baking soda. Pour onto cookie sheets; spread as thin as possible. Cool completely; break into pieces. Store in airtight container in cool dry place.
