Preheat the oven to 350°F. Line a 9×13 baking dish with parchment paper with enough overhang to easily lift out. Set aside.
In a large bowl, melt the butter. Add the flour, sugar, and salt and mix until just combined and crumbly. Transfer the dough into the prepared baking dish by crumbling it into a somewhat even layer. Then, use your hands to press the mixture evenly into the bottom of the pan. Bake for 20 minutes until lightly golden.
In the meantime, prepare the filling. In a small saucepan, bring dates and water to a boil over high heat. Add the baking soda and stir occasionally, until the liquid has evaporated and the dates have melted and thickened, about 5 minutes. Remove the pan from the heat. Transfer the date paste to a large bowl and set aside to cool for 10 minutes.
Add the brown sugar, eggs, vanilla, and salt on top of the date paste in the bowl. Whisk until fully combined, then use a rubber spatula to fold in the chopped pecans.
Remove the crust from the oven and pour the pecan mixture on top. Return to the oven and bake for 30 minutes, or until the center is set.
Allow the bars to cool completely in the pan, about 2 hours. Cut into 24 bars.