Preheat oven to 350 degrees F. Butter and flour a 10-cup Bundt pan. Using an electric mixer, cream the butter for 1 minute, then add the sugar slowly, beating constantly at medium speed for 2 minutes. Beat in the eggs. Stop the mixer and add the flour, baking soda, baking powder, pinch of salt, buttermilk, and orange zest. At medium speed, beat 2 minutes longer. Pour the batter into the greased pan and bake for 40 minutes, or until a knife inserted into the center of the cake comes out clean. Remove the pan from the oven, place onto a cake rack, and let rest for 10 minutes. Invert the cake on the rack and let it cool completely.