Preheat the oven to 350℉. Spread the pecans in an even layer on a sheet pan. Bake for 5–7 minutes or until they smell fragrant. Watch carefully—you don't want to burn them. Remove from the oven and allow to completely cool before transferring them to a mini food processor or cutting board. Pulse on the "chop" setting or finely chop. You want very small pieces but avoid over-pulsing in the food processor or you'll end up with pecan butter.
In a stand mixer bowl with the whisk attachment or a large bowl with a hand mixer, combine the butter and 3/4 cup of powdered sugar. Cream together until smooth and creamy, about 3–4 minutes. Add the vanilla, salt, cornstarch, and chopped pecans, then beat until well combined. Gradually add the flour and mix slowly until smooth. Finally, incorporate the chocolate chips; the mixture may appear sandy and crumbly at first, but keep mixing until it comes together. Avoid overmixing once combined.
Wrap the dough in plastic wrap and refrigerate for at least 1 hour, closer to 12 hours preferred.
After being chilled, measure out cookie dough into 1-tablespoon balls. If the dough gets too warm from being rolled or sitting in a warm kitchen, put it in the freezer for 10–15 minutes. Preheat the oven to 375℉. Line a light-colored sheet pan with parchment paper or a silicone baking mat (see note 1). Bake for 7–11 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 minutes.
Add 1 cup powdered sugar to a bowl and add more as needed. Roll the warm cookies in the powdered sugar and then return to the wire cooling rack. Let cool a few more minutes and then roll in the powdered sugar again.
Notes
Note 1: I tested this recipe with an unlined pan, with parchment paper, and with a silicone baking mat. The cookie bottoms turned out best using the silicone baking mat. The darker the pans, the darker the bottoms of the cookies. The best results I found were with a light-colored pan.Nutrition: The nutrition information includes 1-1/2 cups of powdered sugar coating the baked cookies. You may not use all of the sugar, and that will affect the final nutrition information.Storage: Store in an airtight container at room temperature. Re-roll in additional powdered sugar as needed. Best enjoyed within 3 days.