Place oven racks in lower and upper thirds of oven and preheat to 350 degrees F. Spread the pecan pieces on a large rimmed baking sheet and toast in the oven for about 6-9 minutes, until they are golden and fragrant. Let the nuts cool slightly, then transfer them to a cutting board and coarsely chop them.

Line two baking sheets with parchment paper or silicon baking sheets. If using parchment then give it a quick coat with non-stick cooking spray. Whisk powdered sugar, cocoa powder and salt in a large bowl. Stir in the chopped chocolate and toasted pecans. Then whisk the egg whites and vanilla into the dry ingredients until just incorporated. Spoon the batter by the tablespoonful onto the lined baking sheets, spacing 2-3 inches apart. An ice cream scoop is a good tool to use.

Place the trays into the oven and bake rotating sheets once, after 5 minutes. Bake the cookies until the tops are dry, cracked and set just around the edges, 14-16 minutes. They will look a bit underdone. Transfer the baking sheets to wire racks and let cookies cool on the pan. They’ll firm up when they cool. Cookies can be baked 3 days ahead and stored in and airtight at room temperature.