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

In a medium bowl, combine the flour, 1/2 cup brown sugar, and salt. Add the 3/4 cup of softened butter. Use a pastry blender or your fingers to mix until the mixture resembles coarse crumbs.

Press the crust mixture firmly and evenly into the bottom of the prepared baking pan.

Bake the crust for 15 minutes or until the edges are just barely golden.

While the crust bakes, prepare the filling. In a large bowl, whisk the eggs until lightly beaten.

Add the 1 1/2 cups brown sugar, corn syrup, 3 tablespoons of melted butter, and vanilla extract to the eggs. Whisk until the mixture is smooth and the sugar has mostly dissolved.

Stir in the chopped pecans until they are evenly coated with the syrup mixture.

Pour the filling over the hot, pre-baked crust, spreading the pecans out evenly with a spatula.

Return the pan to the oven and bake for 30 to 35 minutes. The filling should be set around the edges and only slightly jiggly in the center.

Remove from the oven and place the pan on a wire rack. Allow the bars to cool completely in the pan for at least 2 hours before lifting them out by the parchment paper and slicing into squares.