Preheat oven to 300f degrees. Line the bottom of an 8×8 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, cool for a few minutes.
Then cut into squares.