Preheat the oven to 350F, then line a 9x13 pan with parchment so the bars lift out easily after baking. Your oven should be fully heated before you start baking the crust.

Combine all-purpose flour, powdered sugar, cornstarch, and salt, then cut in cold unsalted butter until the dough just comes together. Stop mixing once you no longer see dry flour and the mixture looks crumbly with small butter pieces.

Press the shortbread dough firmly and evenly into the prepared pan, using the bottom of a measuring cup to compact it if needed. Keep the thickness uniform so it bakes into an even base.

Bake at 350F for 18-20 minutes, until the shortbread is pale golden. Look for light color around the edges and a set, lightly dry surface.

Melt unsalted butter, brown sugar, honey, and heavy cream over medium heat in a saucepan. Stir until the sugar dissolves and the mixture looks smooth and glossy.

Bring the mixture to a boil and cook for 2 minutes over medium heat, stirring constantly. Watch for bubbles that hold their shape briefly before they pop.

Remove from the heat and stir in salt, vanilla extract, and whole pecans. The pecans should be evenly coated and the filling should look thick and slightly shiny.

Pour the pecan filling over the hot shortbread and spread it into an even layer. Bake at 350F for 20-25 more minutes until the filling is set and no longer wobbles in the center.

Sprinkle flaky sea salt over the warm bars for a crisp, salty contrast. Use a light hand so the topping stays visible without overpowering the sweetness.

Cool completely before slicing so the filling firms up for clean bars. Once cool, cut into 24 pieces with a sharp knife for straight edges.