Combine first 5 ingredients in a large saucepan. Cook over low heat until sugar dissolves, stirring constantly. Continue cooking over low heat until a candy thermometer registers 234° (about 10 minutes); stir occasionally. Remove from heat; let stand 5 minutes.
Stir in nuts, butter, and vanilla; beat with a wooden spoon until mixture begins to lose its shine (about 6 minutes). Drop by teaspoonfuls onto wax paper. Let stand 20 minutes or until set.
Note: Store pralines in an airtight container for up to 2 weeks.