Grease a 10-cup bundt or ring pan very well and set aside.
Preheat oven to 325°F/165°C, convection/fan forced setting (if you don’t have a convection setting, use 340°F/170°C).
Beat the butter, sugar and zest on medium speed in a stand mixer until it’s smooth and fluffy, about 4 minutes.
1 1/2 cups unsalted butter, 2 cups superfine sugar, 2 lemons, 1 lime
Add the cream cheese and beat until completely smooth and combined, then add the sour cream and vanilla, mixing until combined and creamy. Scrape down the sides and bottom of the bowl once or twice during the mixing.
8 oz cream cheese, 1/2 cup sour cream, 2 tsp vanilla extract
Mix the eggs in one by one, letting each egg fully mix in before adding the next. The idea is to mix the eggs in without overbeating the mixture. It may appear curdled by the time all the eggs are added, but don’t worry as it will come back together once the flour is added.
6 eggs
Add the flour, baking powder and salt. Mix on low speed until just combined, then stop the mixer and give everything a final stir by hand with a spatula, making sure to get to the bottom of the bowl where the mixer blade may have missed.
3 cups cake flour, 1/2 tsp baking powder, 1/2 tsp salt
Scrape the batter evenly into your greased pan and bang the pan on the counter once or twice to bring up any air bubbles. Bake until it tests clean with a skewer, about 1 hour and 35 minutes. If the cake looks like it’s browning too much, you can cover the top with aluminium foil partway through cooking.
Remove cake from the oven and allow to cool for about an hour in the pan, then turn out onto a serving plate and allow to cool completely. Don’t wait to turn it out until it’s cold, as it’ll stick in the pan (ask me how I know this!).
Either dust the cake with powdered sugar or glaze it with a mixture of powdered sugar and lemon or lime juice. For a glaze, you’ll need about 2 cups powdered sugar and enough juice to create a pouring cream consistency.