Preheat your oven to 350°F (175°C). Line a 9x13-inch metal baking pan with parchment paper, leaving a 2-inch overhang on the sides for easy lifting later.

In a food processor or large mixing bowl, combine all-purpose flour, powdered sugar, cubed cold butter, sea salt, and vanilla. Pulse or cut with a pastry cutter until fine crumbs form and press together easily when pinched.

Transfer crumb mixture into prepared baking dish. Press firmly into an even, compact layer across the bottom using the flat bottom of a measuring cup.

Bake at 350°F (175°C) for 18 to 20 minutes until the edges are lightly golden and set. Remove from oven and let sit while preparing the caramel topping.

In a medium heavy-bottomed saucepan over medium heat, combine melted butter, packed brown sugar, maple syrup, and heavy cream.

Bring mixture to a gentle boil, stirring constantly with a wooden spoon or silicone spatula. Allow it to bubble for exactly 2 minutes to emulsify and slightly thicken.

Remove from heat immediately. Stir in the pure vanilla extract and fold in all 3.5 cups of chopped pecans until thoroughly coated in luscious glistening caramel.

Pour the warm caramel pecan filling evenly over the warm par-baked shortbread crust, spreading it to the very edges with an offset spatula.

Return pan to the oven and bake at 350°F (175°C) for 18 to 20 minutes, until the caramel filling is bubbling across the center and fragrant.

Remove from the oven and immediately sprinkle evenly with flaky Maldon sea salt. Allow bars to cool completely at room temperature for 2 hours, then refrigerate for 1 hour for clean, razor-sharp slices. Lift out using parchment handles and slice into 16 or 24 neat squares.