For the shortbread crust:

1. 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.
2. 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. 
3. 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.

For the pecan pie bar filling:

1. 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. 
2. 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.
3. 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.