Preheat oven to 375 degrees. Line a 9×9 baking pan with parchment paper. Set aside.
Beat together softened butter and brown sugar with electric mixer until fluffy. Add salt and stir to combine.
Working in ½ cup batches, add flour, mixing well after each addition.
Press dough into bottom of prepared pan. Prick all over with a fork and then chill in the refrigerator for 20 minutes.
Remove from refrigerator and bake in preheated oven for 20 minutes. Cool completely (I cool mine for 10 minutes and then place in the freezer for 15 minutes to cool quickly).
To make the filling: Combine butter, brown sugar, granulated sugar and heavy cream in medium saucepan over high heat. Bring to a boil and, stirring constantly, boil for 2 minutes. Remove from heat and stir in salt, pecans and vanilla. Pour into cooled crust.
Reduce oven temperature to 325 degrees.
Bake pecan pie bars for 15-20 minutes or until filling is bubbly and the sides are lightly browned. Cool completely before cutting.