Preheat oven to 325 degrees.
Using an electric mixer with a paddle attachment, cream the butter and sugar until light and fluffy. Beat in eggs, one at a time. Add vanilla. Sift together the flour and salt and add to butter mixture. With the mixer running, slowly add buttermilk. Beat four to five minutes, until the batter is very smooth. Pour into a large buttered and floured loaf pan. Place in the center of the oven and bake for one hour and 20 minutes. Be very careful not to slam the oven door, or disturb the cake in any way while baking, or it will fall. A toothpick should come out clean when done.
Yield: 1 large loaf