Heat oven to 350 degrees F. Coat baking dish with a thin layer of butter. Line baking dish with aluminum foil, taking care that the corners and edges are neat and completely covered.
To the bowl of a food processor**, add all shortbread crust ingredients. Pulse until the texture of course sand. The mixture will be very dry.
Dump shortbread mixture into the prepared baking dish and use a rubber spatula and/or clean hands to press it down into an even, firmly packed layer. Pay particular attention to the edges and corners. Bake crust for 16 minutes and set aside.
In a medium mixing bowl, combine brown sugar, gluten-free flour and salt; whisk until mixed. Add corn syrup, eggs and vanilla; mix well. Stir in coarsely chopped pecans.
Spread pecan pie filling evenly over the partially baked shortbread crust. Add extra pecans to empty spots. Bake for 24-30 minutes or until filling is set. The top of the pie bars will be a deep golden brown.
Refrigerate 1-2 hours and then slice into bars. Store covered in the refrigerator for up to 3 days or in an airtight sealed container in the freezer for up to 3 months.
