To toast the pecans, spread them in a single layer on a shallow pan and bake at 300°F (148°C) for 10-15 minutes, stirring once or twice. Allow them to cool completely before chopping.
Beat the butter on medium speed for 30 seconds. Add 1/4 cup of powdered sugar and beat until combined, scraping down the sides as needed.
Add the water and vanilla extract, and beat well. Slowly add in the flour and beat as much as you can. If it becomes difficult to mix, stop the mixer and use a wooden spatula. Stir in the remaining flour and chopped pecans. If needed, use your hands to mix until all ingredients are well combined.
Transfer the dough to plastic wrap, roll it up tightly, and chill for 30-60 minutes, or until the dough is firm.
Preheat the oven to 325°F (160°C) and line a baking sheet with parchment paper. Shape the dough into 1" (2.5cm) balls and place them 1" (2.5cm) apart on the baking sheet. Bake for 15 minutes or until the bottoms are slightly browned. Transfer to a wire rack to cool completely before dusting with powdered sugar.
Notes
This recipe is halved from the original recipe. To store the cookies, layer them between waxed paper in an air tight container. If you preferred, you can use non-toasted pecans.