Preheat your oven to 350°F (175°C).
Line a baking sheet with parchment paper.
In a mixing bowl, combine the egg whites and lemon juice. Beat until soft peaks form.
In another bowl, whisk together the hazelnut flour, sugar, and salt. Add almond extract if using.
Gently fold the dry ingredients into the whipped egg whites.
Scoop a tablespoon of cookie dough, flatten it, place Nutella in the center, and seal the dough around it.
Dust the tops with confectioners' sugar.
Bake for 10-12 minutes until lightly golden and firm.
Allow to cool on the baking sheet before transferring to a wire rack.
