Preheat oven 360°F (180°C) FAN.
Grease and line 2 x 20cm (8 inch) round baking tins with greaseproof paper.
Start by adding the margarine and sugar to a food processor and mix until light and fluffy.
With the mixer on low, add the eggs a little at a time, making sure the eggs are fully incorporated before adding the next egg. You can add a little flour if you notice the mix is splitting slightly. Add the vanilla extract at this stage too.
Sift the flour and add the baking powder before folding both into the mix with a large metal spoon. This will help keep the air in the mixture for a lighter sponge.
Divide the sponge mix equally into the 2 baking tins.
Place the tins on the same shelf in the oven for 30-40 minutes. Once cooked, the cake should be golden browned (you can check the middle is done by inserting a skewer and checking if it comes out clean).
Carefully remove the sponges for the baking tins, removing the grease proof paper and allow to cool on a rack.