1Heat oven to 400ºF. Lightly grease cookie sheet. In large bowl, beat 1/4 cup butter, the brown sugar, sour cream, 1/2 teaspoon vanilla and the egg with spoon. Stir in flour, baking soda and baking powder. Stir in dates and nuts.
2Drop dough by teaspoonfuls onto cookie sheet. Bake about 10 minutes or until golden brown. Remove from cookie sheet to wire rack. Cool completely, about 1 hour.
3Meanwhile, in 2-quart saucepan, melt 1/2 cup butter over low heat. Stir in powdered sugar and 1 teaspoon vanilla until blended. Stir in water, 1 tablespoon at a time, until frosting is smooth and spreadable. Spread cooled cookies with Vanilla Frosting.