In a large bowl, sift the flour and add in the butter. Mix with your hands until everything is combined and a dough is formed. Do not overmix or the butter will melt.
Wrap the dough in a cling film and refrigerate for at least 30mins.
In the meantime, preheat the oven to 180°C / 356°F.
After 30mins, take out the dough and use a rolling pin to roll it out until it's about 5mm thickness.
Using a 3.5cm round cookie cutter, gently cut out round shape biscuits then transfer onto a baking tray.
Re-shape any leftover dough and repeat steps 4-5 above to make more biscuits.
Bake in the oven for 18–20mins or until lightly golden.
Once done, set the biscuits aside on a rack. Let them cool down completely before assembling the napolitaines.
The icing
In a medium bowl, sift the pure icing sugar and cocoa powder.
Add in 1 tbsp of cold water at a time while stirring.
The icing sugar will melt gradually until a thick and glossy consistency is reached. See video for consistency.
Assemble the napolitaine
Spread some nutella on one side of a biscuit and place another biscuit on top of the nutella.
Slowly pour the icing mixture over the biscuits to coat the top and all sides.
Let the napolitaines set at room temperature and enjoy!