Preheat oven to 350°F. In the bowl of a stand mixer fitted with the whisk, or with a hand mixer, combine the butter and sugar. Cream together until combined and soft, about 3 minutes.
Add the eggs and beat until combined. Add the milk. Continue mixing until incorporated.
Add the flour, baking powder, lemon zest and vanilla extract. Beat until mixture is smooth.
Add mixture to a buttered and floured bundt pan. Bake for 35-40 minutes. Remove from the oven.
After 10 minutes invert the cake on to a wire rack. Dust the imperfect side with powdered sugar.
Notes
I used this ring mold pan (10 inches by 3 inches), but you can use any bundt pan you'd like
Traditionally, a ciambellone is served with the imperfect side up. If you'd like, you can serve it with the perfect side up, it's up to you!