Preheat oven to 300°F. Grease and flour a 10-inch tube pan (12-16 cup capacity).
Cream butter and cream cheese at medium speed until well combined, about 2 minutes.
Gradually add sugar, beating until light and fluffy, about 5 minutes. Scrape down sides as necessary.
Add eggs one at a time, mixing well after each addition. Stir in vanilla.
Mix together flour and salt; gradually add to butter mixture, beating at low speed until smooth and well mixed, about 2 minutes. Pour batter into prepared pan.
Fill a 13x9 baking pan with 2 cups of water and place the pan on an oven rack below cake pan.
Bake cake for 90 minutes, or until a toothpick inserted near center of cake comes out clean.
Cool the cake in the pan on a wire rack for 15 minutes.