For crust: In a medium bowl, whisk together flour, sugar, and salt. Using a pastry blender or 2 forks, cut in cold butter until mixture resembles coarse crumbs. Stir in cold buttermilk, 1 tablespoon at a time, until a dough forms.
Turn out dough onto a lightly floured surface, and shape into a rectangle. Wrap in plastic wrap, and refrigerate until firm, at least 30 minutes.
On a lightly floured surface, roll dough into a 17×12-inch rectangle. Transfer to a 15×10-inch rimmed baking sheet, pressing into bottom and up sides. Fold edges under, and crimp as desired. Top with a piece of parchment paper, letting ends extend over edges of pan. Add pie weights.
Bake for 20 minutes. Carefully remove paper and weights. Reduce oven temperature to 325°.
For filling: Sprinkle pecans and chocolate chips in prepared crust.
In a large bowl, whisk eggs until foamy. Whisk in brown sugar, corn syrup, melted butter, flour, salt, and vanilla until well combined. Pour onto pecans and chocolate.
Bake until crust is golden brown and filling is set, 50 minutes to 1 hour, loosely covering with foil to prevent excess browning, if necessary. Let cool completely on a wire rack. Store in an airtight container for up to 3 days.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/pecan-slab-pie-recipe/