Preheat the oven to 180 degrees C/ gas mark 4.
Grease and line a cake tin. Coat the sides of the tin with butter/ oil.
Break the eggs into a large bowl, add in sugar and vanilla essence, whisk until light and fluffy. Pour in oil and milk, and continue whisking.
Now, fold in flour and baking powder until everything is well combined.
Pour the batter into the prepared tin and bake for 30-40 minutes until the cake is golden-brown and coming away from the edge of the tin. Press gently to check, it should be springy to the touch. Remove it from the oven and set aside to cool for 10 minutes.
Then run a palette or rounded butter knife around the inside edge of the tin and carefully turn the cakes out onto a cooling rack. Yummy sponge cake is ready to serve!