Mix together buttermilk and polenta; let soak for 45 minutes. Preheat oven to 350°F. Butter and flour two 8" tube cake pans. Stir in rosemary. Cream together butter and sugar until white and fluffy. Add eggs 1 at a time, beating well after each addition.
Fold soaked polenta and dry ingredients alternately into creamed mixture, in 3 additions. Divide batter between prepared pans. Bake about 40 minutes, or until a toothpick inserted into cake comes out clean. Let cakes cool about 5 minutes before turning out onto a wire rack to cool.
