Chewy, fudgy cookies with a crackly, salted top. Crisp exterior, brownie-like middle, laced with Nutella, and dotted with crunchy salt, it's cookie nirvana.
Preheat the oven to 350 degrees. Line 2 large baking sheets with parchment paper or silicone mats.
In a large bowl, whisk together 2 cups of the powdered sugar, brown rice flour, cocoa, cornstarch, and salt. Set aside.
In a mixing bowl, beat together the butter and remaining cup of powdered sugar until blended. Beat in the egg whites and egg. Beat in the Nutella and vanilla. Gradually beat in the powdered sugar/brown rice flour mixture until blended. Fold in the chocolate chips.
Spoon the batter onto the prepared baking sheets - use a cookie scoop or heaping tablespoon for each cookie, leaving about 2 inches between cookies (you'll need to work in batches to prevent overcrowding the pans - I used 4 cookie sheets total, 6 cookies per pan).
Bake for 10 to 12 minutes, until the tops are crackly and the edges are set. Cool on wire racks before sprinkling with the sea salt.