Preheat oven to 350°. Grease a large Bundt pan well.

Using a mixer, cream the butter until very light and smooth. Add cream cheese and beat another 2 to 3 minutes. Add sugar very slowly to the butter mixture and continue to mix until well incorporated. Add the eggs, one at a time, to the butter mixture. Add vanilla and the lemon and orange rinds, mixing until well incorporated.

In a separate bowl, sift together the flour, baking powder, baking soda, and salt. Taking turns, add small amounts of the flour mixture and then the ricotta cheese, mixing to incorporate. Pour batter into pan and bake 60 to 70 minutes, or until a toothpick inserted comes out clean. Cool and dust with powered sugar.