Preheat oven to 350 F. In large mixing bowl, cream together butter and sugar. Blend in sour cream and vanilla beating until smooth. Beat in eggs, one at a time. Stir flour with baking powder, soda and cornstarch; blend into creamed mixture. Pour into greased and floured bundt pan. Bake at 350 F. for 55 minutes. Shut off heat and cool in open oven for 20 minutes. Remove from pan and finish cooling on rack.
Please note that some ingredients and brands may not be available in every store.