Place the hazelnuts in a bowl. Beat the egg whites, salt, vanilla paste and cardamom until stiff. Spoon in the sugar and continue beating until the mixture turns glossy. Carefully fold the egg whites into the nuts in layers. Using a teaspoon, place 30 walnut-sized mounds on a baking tray lined with baking paper. Press one hazelnut into the centre of each biscuit.
Leave to dry at room temperature for approx. 6 hrs.
Bake for approx. 10 mins. in the centre of an oven preheated to 175°C. Allow to cool and dust with icing sugar.