Sift together flour, soda and salt and set aside. Cream together butters. Gradually add sugars. Add egg and vanilla. Blend in dry ingredients. Form into balls using a teaspoon of dough for each. Roll in granulated sugar and place on ungreased cookie sheets. Bake at 350° for 8 minutes. Place a chocolate kiss on top of each cookie until it cracks around the edges. Bake 2-5 minutes more until golden brown.