Preheat the oven to 350 degrees F and line a 9x9" baking sheet with parchment paper.
Combine butter, flour, and sugar for the crust with a mixer or pastry cutter until crumbly (it won't be a smooth dough but should hold together when you squeeze it - if not, add a tablespoon of water). Press firmly into the bottom of the prepared pan.
Bake for 10–12 minutes, or until it looks slightly puffed and dry. Remove from oven and let cool slightly while you prepare the filling.
In a medium bowl, whisk together brown sugar, corn syrup, melted butter, eggs, vanilla, and salt. Stir in the pecans.
Pour the filling over the baked crust and continue baking for 20–25 minutes, just until the filling is set (a slight jiggle in the center is all right, as they will set as they cool).
Let it cool completely before slicing. I like to refrigerate for a few hours before slicing to get clean edges.
