Preheat the oven to 325°F. Grease a 10-inch tube pan.
Cream the butter and sugar together in a mixing bowl until light and fluffy. Beat in the eggs, one at a time, blending well after each addition.
Sift together the flour, baking soda, and salt. Stir the dry ingredients into the egg mixture alternately with the buttermilk, beginning and ending with the dry ingredients. Add the lemon zest and juice.
Pour the batter into the prepared tube pan. Set the pan on the center rack of the oven and bake until the cake pulls away from the sides of the pan and a tester inserted in the center comes out clean, 1 hour and 5 minutes.
Cool the cake in the pan, set on a rack, for 10 minutes. Remove the cake from the pan and spread on the icing at once, while the cake is still hot.