Preheat oven to 175°C (350°F) and grease a cake pan lightly with butter or oil.
In a large bowl, cream together butter and sugar until light, fluffy, and pale.
Add eggs one at a time, mixing well after each addition.
Stir in vanilla extract and citrus zest until fully combined.
In a separate bowl, sift together flour, baking powder, and salt.
Gradually add dry ingredients into the wet mixture, alternating with milk. Mix gently until smooth.
Pour batter evenly into the prepared cake pan.
Bake for 30–40 minutes or until a toothpick inserted in the center comes out clean.
Remove from oven and let cool in the pan for 10 minutes, then transfer to a cooling rack.
Serve plain or frost as desired.
