Set 3 tablespoons of sugar aside. Add the remaining sugar, almond flour, flour, orange zest, almond extract (if using), and icing sugar to a bowl and mix briefly.
Pour the water into a saucepan with the remaining 3 tablespoons of sugar, and simmer over low heat, stirring, until the sugar has dissolved. Remove from the heat, allow to cool slightly, then pour it into the bowl with the almond mixture.
Cover the bowl with cling film and let it rest at room temperature for at least 1 hour or overnight. This step is optional but recommended as it will make the cookie dough more aromatic.
Whisk the egg white until foamy then add into the bowl with the remaining ingredients. Add baking powder and mix all the ingredients together to form a slightly sticky dough.
Preheat oven to 160°C/320°F and or with the fan option on at 140°C/280°F, and arrange the baking tray onto the middle shelf of the oven.
Sprinkle a work surface with icing sugar, and roll the dough into a log.
Cut into slices about 1,5 cm-½-inch thick, and give each slice the classic oval shape of the ricciarello. As you make them, dust them on both sides with icing sugar and arrange them on the baking tray lined with parchment paper. Bake the cookies for about 10-12 minutes. As soon as the cracks begin to form on the surface, they are ready and you can take them out of the oven.
Do not worry if they seem too soft, when they get cold they will reach the right consistency. Transfer the cookies to a cooling rack and allow them to cool completely, then serve.