Step 1: Preheat the oven to 180°C conventional oven (356° Fahrenheit/Gas 4). Adjust the metal racks to the middle groove of the oven. Line a baking tray with baking paper.
Step 2: Using a stand mixer (with flat beater attachment) or electric mixer, beat the egg, sugar, yoghurt, oil, vanilla bean paste and salt until just combined. Add in the flour, tablespoon by tablespoon until just combined. Add the baking powder and lemon zest into the mixture until just combined.
Note: 00 is a powder-fine Italian type of flour. It is made from soft wheat varieties, and is frequently used in Italian desserts and pastas. 00 flour is available in most supermarkets, Italian food stores and gourmet delicatessens.
Step 3: Roll 60g of dough into a ball. Flatten slightly into an oval shaped biscuit. Place the 5 tablespoons of remaining sugar into a small bowl. Coat the biscuits in sugar and place onto the prepared baking tray. Repeat with the remaining biscuit dough.
Step 4: Cover the tray of biscuits with plastic wrap and refrigerate for 15 minutes.
Step 5: Remove the biscuit tray from the fridge. Sift the icing sugar over the biscuits.
Step 6: Bake on the middle groove of the oven for 20 minutes. Cool before serving – buon appetito!.