Position rack in center of oven and preheat to 350 degrees. Line 2 baking sheets with parchment. Stir butter, sugar, corn syrup in heavy medium sauce pan over low heat until melted and smooth. Bring to boil over medium high heat, stirring constantly. Remove from heat. Stir in flour. Add nuts and vanilla. Stir to combine. Drop by teaspoonfuls onto prepared baking sheets, spacing 2” apart. Bake, 1 sheet at a time until bubbly and lightly browned, about 11 minutes. Cool on sheets 10 minutes. Transfer to rack. Cool completely.