Adjust an oven rack to the middle position and preheat the oven to 325 degrees F. Line 2 baking sheets with parchment.
Whisk the flour and salt together in a large bowl and set aside.
Combine the butter and granulated sugar in a separate large bowl and beat with an electric mixer on medium-high speed until light and fluffy, 3 to 4 minutes. Beat in 4 teaspoons of water and the vanilla. Slowly mix in the flour mixture and finally, the pecans.
Break off tablespoonful pieces of dough, roll each to form a crescent shape and arrange evenly spaced on the prepared baking sheets. (You'll have leftover dough for a second batch.)
Bake until slightly golden on the bottoms and edges, 10 to 12 minutes. Watch very carefully--better to undercook than overcook. Let the cookies cool on the baking sheets for a few minutes, then transfer to a wire rack to cool completely, about 10 minutes. Repeat with the remaining dough.
Put the powdered sugar in a shallow plate. Once cooled, roll each cookie in an ample amount of the sugar.
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