In a bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add eggs, 1 at a time, beating well after each addition. Combine flour, baking soda and salt; add to creamed mixture alternately with sour cream and vanilla. Beat on low just until blended. Pour into a greased and floured 10-in. fluted tube pan. , Bake at 325° for 1-1/4 to 1-1/2 hours or until a toothpick comes out clean. Cool in pan 15 minutes before removing to a wire rack to cool completely. Sprinkle with confectioners' sugar if desired.