Preheat oven to 350 degrees F. Line an 8 inch square metal pan with nonstick foil. If you don't have any of the foil you can use regular foil and spray it with cooking spray.
In a microwave-safe bowl, melt the butter gently using one of the lower heat settings (50% power) until it is melted.
In a mixing bowl, combine the melted butter with the brown sugar, vanilla extract and salt. Stir well, then add the flour and stir until blended. Measure out a packed half cup or weigh out 100 grams and put it in a a separate bowl.
Press remaining shortbread dough into bottom of the pan and bake for 15 minutes or until set and lightly browned around edges.
When the crust is done, reduce heat to 300 degrees F.
Meanwhile, add 3 tablespoons of flour (24 grams) to the reserved 1/2 cup of dough and crumble it all together so that you have a topping.
Combine the filling ingredients (melted butter, dark corn syrup, granulated sugar, egg, vanilla and pecans) and stir well, then pour over the baked crust.
Sprinkle the topping mixture over the pecan mixture.
If you haven't already reduced the heat, make sure it is at 300 degrees F.
Bake the bars for about 40-45 minutes or until top is slightly browned and bars are firm.
Let the bars cool for 20 minutes in the pan. Use foil as a handle and lift from pan, then score into 12 bars (do not separate yet) and let cool completely.