Prepare the pan: Line a 9x13-inch pan with parchment, leaving overhang on two sides for easy lifting. Lightly grease the parchment.
Heat the oven: Preheat to 350°F (175°C).
Spread the pecans on a baking sheet and toast for 6–8 minutes, until fragrant. Cool slightly, then chop if desired.
Make the crust: In a bowl, cream the softened butter and granulated sugar until smooth. Mix in the salt, then add the flour and stir until a soft dough forms.
Press and bake the crust: Press the dough evenly into the lined pan.
Prick with a fork a few times. Bake for 15–18 minutes, until the edges are just turning golden.
Whisk the filling: In a large bowl, whisk the eggs. Add brown sugar, syrup, melted butter, vanilla, and salt.
Whisk until smooth and glossy. Stir in the toasted pecans.
Assemble: Pour the filling over the hot crust and spread the pecans evenly. If using, sprinkle a pinch of flaky sea salt on top.
Bake: Return to the oven and bake for 22–28 minutes.
The center should be set but slightly jiggly, and the edges should be firm. Do not overbake.
Cool completely: Let the pan cool on a rack to room temperature, then chill for 1–2 hours for the cleanest slices.
Slice and serve: Lift out using the parchment overhang. Use a sharp knife to cut into bars.
Wipe the blade between cuts for neat edges.