Preheat oven to 200°C

Grease a 30 x 40 cm baking tray with vegetable oil .Cut a piece of parchment paper to fit inside the baking tray.

Using an electric mixer with a paddle attachment place the butter,sugar and zest,cream together until pale in colour and fluffy.

Beat the eggs lightly in another bowl and slowly add to the mix (while padding on medium speed),until well combined.

Bring down the speed of the mixer and gradually add in the flour.

Evenly fill the baking tray with the cake batter,using a palette knife.