Beat the egg whites until soft peaks form, then add the granulated sugar and beat until stiff peaks form. Add the powdered sugar, almond flour, cocoa, and salt and mix well.
Leave to sit uncovered for 30 minutes. Meanwhile, prepare your baking sheets by lining with a silicone mat or parchment paper. Fit a piping bag with a round tip. Preheat the oven to 325F.
Fill the piping bag with the batter and then drop 1-inch rounds on the baking sheet.
Bake for 10 - 11 minutes, turning halfway. Allow to cool for 20 minutes, then transfer to a wire rack. Allow to cool completely.
Place a small dollop of dulce de leche on top of half the cookies. Sprinkle fleur de sel over the dule de leche and top with the remaining brownie cookies.