Brown the butter, decant, then measure 6 tablespoons. In clean saucepan, mix brown butter, brown sugar, golden syrup and salt. Bring to a simmer and cook for 2 minutes. Stir in pecans, cider vinegar, vanilla and bourbon. Let cool slightly, then whisk in eggs.
Pour mixture into prepared pie shell and bake at 350°F (175°C) for 40 to 45 minutes. Cool on a rack and serve slightly warm or at room temperature.
