Preheat oven to 300° degrees. Line the bottom of an 8x8 baking pan with parchment paper. In a small bowl, mix butter, sugar, vanilla, and flour until you have a thick, sticky dough.
Press into the bottom of prepared baking dish in a single thin layer and bake at 300f degrees for 10-15 minutes.
In a large bowl, mix eggs, brown sugar, corn syrup, and flour until combined. Fold in chopped pecans.
When shortbread layer is done, remove from the oven and pour over your pecan mixture. Raise the oven temperature to 350 degrees, and bake again for 25-30 minutes or until top is golden and crispy.
Take out and allow to cool COMPLETELY. These slice up easier if you put them into the refrigerator and cool. It also helps the filling to finish setting up.
Then cut into squares and serve!