Put the butter, hazelnuts, vanilla extract and 85g of the icing sugar in a food processor and whizz to a paste. Add 1 tsp of the ground cloves and the flour, and pulse together until a dough forms.
Heat oven to 200C/180C fan/gas 6. Line a couple of baking sheets with baking parchment. Roll the dough into walnut- sized balls and arrange on the baking sheets. Use the back of a fork to lightly squash each ball, then bake for 12-15 mins until they turn a pale biscuit colour – if they get too brown, they will become dry.
Mix the remaining icing sugar and ground cloves, then sieve thickly over the hot biscuits. Leave to cool slightly before eating just warm, or cool.