Preheat oven to moderately hot - 190 deg C. Lightly grease 2 or 3 large baking trays then line the trays with baking paper.
Cream butter, sugar and vanilla essence until light and fluffy. Beat in the egg. Add sifted flours and sultanas, making into a soft dough.
Put cornflakes onto a tray or plate, then take rounded teaspoons of the biscuit mixture and drop into the cornflakes. Roll lightly in palms of hands to completely coat the dough with the cornflakes. Place onto prepared baking trays, leaving plenty of room between the biscuits to spread.
Bake in a moderately hot oven for 20 to 25 minutes, or until they look cooked. Loosen biscuits from tray with a spatula while still warm. When cold store in an airtight container.