Preheat your oven to 160°C. Prepare 1 big baking sheet or 2 smaller ones

Beat the egg whites with an electric mixer and beat on until stiff, glossy peaks form. Be careful not to overbeat.

In a separate large bowl, whisk together the almond flour, granulated sugar, confectioners' sugar, and salt.

Gently fold the whipped egg whites into the dry ingredients in two or three additions. Mix until just combined into a thick, sticky paste. Be careful not to deflate the egg whites too much.

Stir in the almond extract and vanilla extract.

If using the almond liqueur, add just little bit so the dough does not get wet and excessively sticky. Also if using almond liqueur, use just 1 tbsp of almond extract instead.

Place some extra granulated sugar and extra confectioners' sugar in two separate shallow bowls if you want a classic cracked appearance.

Wet your hands for the dough to not get sticky, grab 1 tsp of the dough and roll it between your hands, roll it in the caster sugar and then roll it in the icing sugar. Each ball should be around the size of a walnut (3~4 cm). Repeat until the dough is over

Gently press one into the center of each cookie.

Bake for 15-20 minutes, or until the cookies are lightly golden on the outside and the tops are cracked. They should be soft and chewy on the inside