FOR THE CAKE: Preheat oven to 350 degrees F, then grease & flour a 10-inch Bundt pan.
In a large mixing bowl, cream butter & sugar until light & fluffy.
Add eggs, one at a time, beating well after each addition.
Beat in the vanilla.
In another bowl, whisk together flour, baking powder, cinnamon, baking soda, salt & nutmeg, then add this flour mixture to the butter mixture, a cup at a time, & alternating the flour mixture additions with a cup of sweet potato additions. BEFORE COMPLETELY MIXED, add the tablespoon of orange zest, & mix just until combined in a stiff batter.
Pour batter into the prepared pan & bake 50-60 minutes or until a toothpick inserted near the center comes out clean.
Remove from the oven & cool for 10 minutes before removing cake from the pan & placing the cake on a wire rack to cool completely.
FOR THE GLAZE: In a small bowl, combine powdered sugar, 1 teaspoon of orange zest & enough juice to achieve an acceptable consistency.
Drizzle over the cooled cake.