Preheat the oven to 180°C. Line a baking tray with greaseproof paper, then place the sifted icing sugar into a small bowl, ready for coating the pizzicotti. Set both aside for later.
Place the clementine zest, ground almonds and caster sugar into the bowl of a food processor. Pulse a few times to combine the ingredients and break down the sugar and almonds a little.
Add the egg whites, almond extract and honey to the food processor, then pulse until the mixture starts to come together into a sticky dough. Remove the dough from the food processor and transfer to a clean work surface, lightly dusted with icing sugar, then knead gently with your hands until it forms a smooth ball. You can shape and bake the pizzicotti immediately, or you can wrap the dough in cling film at this stage and store in the fridge for up to 2 days.
To shape the pizzicotti, take a small amount of the dough (about 25g) and roll it between your hands to make a ball. Drop the ball into the bowl of icing sugar, then roll it around until it is completely coated. Place the pizzicotti onto the baking tray, then use your thumb, index and middle fingers to gently pinch the ball and give the cookie its characteristic shape. Repeat this process with the remaining dough, spacing them out slightly on the tray (they don't spread hugely, but do give them a little room to grow- if in doubt, use a second tray).
Bake the pizzicotti in the preheated oven for 12-14 minutes, until the cookies (underneath all of the icing sugar!) have turned golden and are slightly cracked. Let them cool completely before removing them from the tray and serving. Stored in an airtight container at room temperature, the pizzicotti will keep for up to two weeks.