Preheat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving an overhang on the two long sides for easy lifting.
Make the crust: In a food processor, pulse the flour, powdered sugar, and salt to combine. Add the cold butter cubes and pulse until the mixture resembles coarse crumbs and just starts to clump.
Press the crust firmly and evenly into the prepared pan, building a slight edge. Prick the surface all over with a fork. Par-bake for 18–20 minutes, until the edges are lightly golden. Leave the oven on.
Make the filling: In a large bowl, whisk the corn syrup, brown sugar, eggs, melted butter, vanilla, and salt until completely smooth and glossy.
Fold the chopped pecans into the filling until every piece is coated.
Pour the filling evenly over the hot par-baked crust, then gently scatter the pecan halves over the top in an even layer.
Bake for 30–35 minutes, until the filling is set at the edges but still has a slight jiggle in the center — it will firm up as it cools.
Cool completely in the pan on a wire rack for at least 2 hours. For the cleanest slices, chill for 1 hour after cooling.
Lift the slab out using the parchment overhang and cut into 24 bars with a sharp knife, wiping the blade between cuts. Serve at room temperature.