Preheat the oven to 180°C/350°F/Gas mark 4
Sift together the flour, salt, baking powder and soda. Cream trogether the butter, sugar and vanilla. Beat until smooth. Add flour mixture and sour cream; stir in cashews.
Drop by tablespoons on ungreased cookie sheet 1-1/2 inches apart. Bake for 8 to 10 minutes. Cool 2 minutes in the oven, then remove to racks. Add frosting when cooled completely.
For the icing, sift the icing sugar/confectioner's sugar into a bowl. Cream in the butter, milk and vanilla. Blend until smooth. Top each cookie with a generous portion.
