1. Preheat the oven to 180C.
2. Butter a 23cm by 33cm pan or two 15cm round pans.
3. In a large bowl, using an electric mixer, cream the butter and caster sugar together.
4. Beat in the eggs, one at a time, then add the lemon zest.
5. In a separate bowl, sift the plain flour, baking powder, bicarbonate of soda and salt.
6. In another bowl, combine the lemon juice, buttermilk and vanilla.
7. Slowly add the plain flour mixture and wet ingredients into the egg mixture.
8. Divide the butter between the prepared round pans or sheet pan.
9. Bake for 45 minutes to 1 hour.
10. Remove from the oven and allow to cool in the pans.
11. Slice, as desired, and serve.
