Cream butter and vanilla; gradually beat in sugar. Add egg and beat until light. Sift dry ingredients, and add alternately with sour cream. Stuff dates with walnut halves, and roll in dough. When well covered, drop from a fork onto a well-greased cookie sheet. Bake in preheated 200ºC oven for about 10 minutes. When cold, spread with icing. ICING: Blend ingredients together. ----