Preheat the oven to 350°F (175°C) if you turned it off after toasting the pecans. The bars will bake briefly before chilling so the sweetened condensed milk layer can thicken and set properly.
Make the butter pecan topping: In a medium bowl, whisk together the sweetened condensed milk, 3 tablespoons melted butter, vanilla extract, and 1/4 teaspoon salt until smooth and glossy.
Fold in about 1 1/2 cups of the chopped toasted pecans, reserving the remaining 1/2 cup for sprinkling over the top. This gives you both a nutty layer inside and a pretty, pecan-studded finish.
Pour the butter pecan mixture evenly over the graham cracker crust in the glass dish. Use a spatula to spread it all the way to the edges so every bar has a good layer of filling.
Sprinkle the reserved chopped pecans evenly over the top, pressing them very gently into the surface so they stick but still sit proudly on top for that glossy, textured look.
Bake the bars at 350°F (175°C) for 18–22 minutes, or until the edges are just starting to bubble and the center looks set but still slightly jiggly. The top should look shiny and glossy, with the pecans lightly toasted.
