Mix the egg whites with lemon juice, vanilla, almond extract and orange zest using a hand whisk for a few seconds until you have a foamy mixture.
Add the almond flour and 200 g of powdered sugar. Mix with a spoon and then with your hands until you have a smooth, soft mixture.
Transfer all the mixture to the center of a piece of plastic wrap, form it into a ball and wrap it tightly, then leave it to rest in the fridge for at least 24 hours up to a maximum of 3 days. Remember that the longer it rests, the more fragrant the mixture will become.
At the end of the indicated time, prepare a large baking sheet and line it with parchment paper. Then sprinkle about 150 g of powdered sugar onto a work surface or cutting board and place the dough on top.
Using your hands, form the dough into a long, wide cylinder about 3 cm thick. Cut it into 25 pieces of about 20 g each.
Now is the time to preheat the oven to 150 °C in static mode.
Take the first piece, dip it in the powdered sugar and shape it into a grain shape with your hands, flattening, shaping and extending the tips.
Transfer the first Ricciarello to the lined baking sheet. Repeat with the remaining Ricciarelli, placing them about 4-5cm apart from each other. You may need 2 or more sheets depending on the size.
Lightly moisten your fingers with water and brush them over the surface of the ricciarelli. Add a layer of about 1mm of powdered sugar and gently press it down with a spoon to smooth it out.
Bake in a preheated static oven at 150 °C for the first 5 minutes, then increase to 170 °C for 5 minutes until the classic cracks form on the surface, then lower to 160 °C and bake for another 5 minutes for a total of about 15 minutes.
Once baked, the Ricciarelli will be soft, so transfer them very gently to a rack, collecting them with a spatula.
Let them cool and rest for about an hour before serving. At this point, the consistency of Siena's Ricciarelli will be perfect!