In medium saucepan, combine butter, egg yolks, brown sugar and salt. Bring to a boil over medium heat, whisking constantly until thickened, about 10 minutes. Remove from heat; stir in maple flavoring and pecans. Transfer to medium bowl; cover surface with plastic wrap to prevent skin from forming. Refrigerate 2 hours or until chilled. Stir before using; chill cupcakes. Refrigerate until ready to serve.