Preheat the oven to 180C/350F/Gas mark 4
Cream the butter with the sugar, add the sour cream and vanilla and beat until light and fluffy. Fold in the sifted flours until blended. Form teaspoons of the mixture into balls, place on greased baking trays, about 5 cm (2") apart and lightly press each biscuit with the back of a fork. Bake for 10-12 minutes for each tray or until golden brown and cool on wire racks. Sandwich Cookies in pairs with the filling.
For the filling, cream the butter and icing sugar in a bowl until light and foamy. Stir in the milk and vanilla. Blend in the sieved jam.
