3 cups / 11 oz / 310 g walnut halves, toasted & cooled
4 cups / 1 lb / 453 g confectioner's (powdered) sugar1/2 cup plus 3 tablespoons / 2 oz / 60 g unsweetened cocoa powderscant 1/2 teaspoon fine grain sea salt
4 large egg whites, room temperature
1 tablespoon real, good-quality vanilla extract
Preheat oven to 320F / 160C degrees and position racks in the top and bottom third. Line three (preferably rimmed) baking sheets with parchment paper. Or you can bake in batches with fewer pans.
Make sure your walnuts have cooled a bit, then chop coarsely and set aside. Sift together the confectioner's sugar, cocoa powder, and sea salt. Stir in the walnuts, then add the egg whites and vanilla. Stir until well combined.
Spoon the batter onto the prepared sheets in mounds of about 2 tablespoons each, allowing for PLENTY of room between cookies. These cookies are like reverse Shrinky Dinks - they really expand. Don't try to get more than 6 cookies on each sheet, and try to avoid placing the batter too close to the edge of the pan.
Bake until they puff up. The tops should get glossy, and then crack a bit - about 12 -15 minutes. Have faith, they look sad at first, then really blossom. You may want to rotate the pans top/bottom/back/front.
Slide the cookies still on parchment onto a cooling rack, and let them cool completely. They will keep in an airtight for a couple day