Preheat the oven to 190C/375F/Gas mark 5
Sift the dry ingredients into bowl. Rub in the butter. Stir in hazelnuts and sour cream. Mix to a firm dough. Turn the dough onto a lightly floured surface. Knead until smooth. Cover and refrigerate for 30 minutes.
Roll the dough between sheets of greaseproof paper until 5mm thick. Cut 5cm rounds from dough. Place the rounds about 3cm apart on greased baking trays. Bake for about 10 minutes or until lightly browned; cool on trays. Drop about 2 level teaspoons of topping onto each biscuit. Refrigerate until set. Makes about 35.
Crunchy Topping: Combine all the ingredients in bowl. Mix well.
