In a large bowl mix the icing sugar and the cubed butter until the sugar is incorporated in the butter. Work with your fingertips so that you don't melt the butter.
Add the flour. Knead the dough briefly until all the ingredients are incorporated and a smooth dough is formed. Wrap in cling film and let it rest in the fridge for at least 30 minutes.
Meanwhile preheat the oven to 180°C or 350°F. Line a baking tray with parchment paper. Set aside.
Roll out the dough on a floured surface until it's about 1 cm thick. Cut the dough into even circles. Transfer to the baking tray, leaving some space between one another, and bake for 15 minutes, until they turn slightly golden brown at the edges.
Leave to cool at room temperature on a cooling rack.
Once all the biscuits have cooled a little, add about a tablespoon of the chocolate ganache to a biscuit and place another biscuit on top.
Sprinkle the sandwiched biscuits with icing sugar.