Step 1

Preheat the oven to 180C/350F/Gas Grease a 13x9-inch pan, and set aside.

Step 2

Whisk together the flour, baking powder, baking soda, and salt. Set aside.

Step 3

Whisk together the eggs. Add the sugar, and whisk until combined. Add the vanilla extract and vegetable oil, and whisk until combined. Gradually mix in the dry ingredients, alternating with the buttermilk.

Step 4

Pour the batter into the prepared pan, and spread out evenly. Bake for 30 - 35 minutes, or until a toothpick inserted into the centre comes out clean. Allow to cool completely in the pan on a wire rack before frosting.

Step 5

Using a handheld or stand mixer, beat together the butter and icing sugar until light and fluffy.

Step 6

Beat in the milk and vanilla extract until smooth, and spreadable. Spread the frosting over the top of the cooled cake, then slice and serve.