Preheat oven to 165C (330F), place oven rack in center of oven. Butter & flour (21cm-23cm) loaf pan
In a large bowl, sift together the flour, baking powder, baking soda, and salt.
Mix sugar with zest (10 minutes) to enhance the flavor.
In the bowl of standing mixer, beat the butter and cream cheese until smooth. Gradually add the sugar, scraping down the sides of the bowl as needed. Add the vanilla, the eggs, one at a time, mixing well after each addition. Scrape down the sides of the bowl as needed. Add the flour mixture, in three additions, and mix just until incorporated. Pour the batter into the prepared pan and smooth the top.
Bake for about 55 minutes until the cake is golden brown and a toothpick inserted in the center comes out clean.
Remove the cake from the oven and place on a wire rack to cool.
