2 tbsp. vanilla extract (yes, that’s 2 tbsp. and not 2 tsp.)
About 1 3/4 lbs. powdered sugar, divided
6 cups flour (see Tips for Success, above)
3 cups finely chopped walnuts
Preheat oven to 300°. Line 2 rimmed baking sheets with parchment paper. Beat butter, vanilla, and 1 cup powdered sugar in the bowl of a stand mixer on medium speed until creamy, well-blended, and fluffy. Add flour 2 cups at a time, beating on low speed, then on medium speed after each addition until well-blended, stopping occasionally to scrape inside of bowl. Add nuts and beat on low speed until blended. Stir by hand a few times to be sure dough is evenly blended. Roll even 1-in. balls of dough in your hands and space 1 in. apart on lined baking sheets. Bake until dough is pale golden on top and golden on the underside, 25 to 35 minutes. Let cool 5 minutes. Gently toss warm cookies a few at a time in a bowl of powdered sugar (the sugar will melt and form a coating), then set on wire racks to cool completely. Repeat to make more cookies. Gently toss cookies in powdered sugar again to coat generously. Store airtight up to 1 week, or freeze.