Maple Popcorn

1 c Maple syrup
3 tb Butter
1 ts Vanilla
8 c Popped corn

Lightly butter a 9"x13" baking pan. Set aside. In a heavy saucepan, combine maple syrup and butter. Bring mixture to a boil. Cook, stirring occasionally, until a candy thermometer reaches 275~ (syrup separates into hard, but not brittle, threads when dropped into very cold water). Remove from heat; add vanilla extract. Pour over popcorn. Pack the mixture lightly into the prepared pan; let cool completely. Cut into small squares.