• Inside a baking tray bake pecan halves for 8 minutes under 300 degrees. Set aside.

Make the crust:

• Adjust oven rack to the lowest position and preheat to 350 degrees F. Line up a 9x13 baking pan with parchment paper and spray with nonstick cooking spray.
• In a medium bowl, whisk together the flour, sugar and salt. Add the melted butter and stir using a wooden spoon until a dough begins to form.
• Using your hands continue to combine until no flour remains and a small portion of dough holds together when squeezed.
• Evenly spread spoons of dough over your baking pan. Using your fingertips, press and smooth dough into an even layer in the bottom of the pan. Set aside.

Make the Filling:

• In a medium bowl, whisk together brown sugar, agave syrup, melted butter, vanilla, and salt until smooth and well combined.
• Fold pecan halves into the sugar mixture until the pecans are evenly coated.
• Pour the pecan mixture over the crust, using a rubber spatula. Spread it working it to the edges and into corners. You will have bare patches and that's okay.
• Bake for about 20 to 25 minutes, until the topping is evenly distributed and rapidly bubbly across the entire surface.
• Transfer pan to a wire rack. Let bars cool completely in the pan, about 1 1/2 hours. Cut into 20 to 24 bars and serve.
• Store bars at room temperature in an airtight container for up to 4 days.