TOAST PECANS: Preheat the oven to 350 degrees F. Spread the pecans in an even layer on the sheet pan. Bake for 5-7 minutes or until they smell fragrant. Watch carefully; you don't want to burn them. Remove and allow to completely cool before transferring them to a mini food processor or cutting board. Pulse or finely chop into very small pieces. Avoid over-pulsing in the food processor or you'll end up with pecan butter.
WET INGREDIENTS: Either in a bowl of a stand mixer with the whisk attachment or a large bowl (and using a hand mixer) combine butter and 3/4 cup powdered sugar. Cream together until smooth and creamy, about 3-4 minutes. Add in the vanilla, salt, cornstarch, and pulsed/chopped pecans. Beat until smooth and combined. Add in the flour and mix until combined and smooth. It will seem sandy and crumbly at first, but keep mixing; it will come together. Once combined, do not overmix.
CHILL: Wrap the dough in plastic wrap and refrigerate for 1 to 2 hours to chill.
BAKE: After being chilled, measure out cookie dough using a 1 tablespoon measuring spoon (each ball should be exactly 1 tablespoon). If the dough gets overly warmed from being rolled or sitting in a warm kitchen, put in the freezer for 10-15 minutes. Preheat the oven to 375 degrees F. Line a light-colored sheet pan with a Silpat liner (Note 3). Bake for 7-11 minutes (mine take 10 minutes). (It's okay if some of the cookies bleed out on the edges and turn brown, this crumbles off easily when ready to roll in powdered sugar). Remove from the oven, let stand on tray for 3-5 minutes and then transfer to a wire cooling rack. Let cool for 2-3 or so minutes.
POWDERED SUGAR: Add powdered sugar to a bowl (I start with 1 cup, but you may need slightly more). Roll the warmed cookie in the powdered sugar and then return to the wire cooling rack. Let cool down a few more minutes, and then roll in the powdered sugar again.
STORAGE: Store in an airtight container at room temperature. Re-roll in additional powdered sugar as needed. Best enjoyed within 1-3 days.