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). 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.