1. Line 2 x 20cm (8 inch) round cake tins with greaseproof paper and grease with butter.
2. Place the margarine and sugar into the food processor bowl and cream until light and fluffy. During processing stop the machine two or three times and scrape down the mixture.
3. Beat in the eggs one at a time.
4. Slowly add the flour down through the feeder chute, mix together until all the flour is incorporated using a pulsing action or low speed.
5. Transfer to the prepared tins and smooth the tops with a knife.
6. Bake in the centre of the oven at 180°C, 350°f, Gas No. 4 for 20 - 30 minutes, or until a wooden cocktail stick inserted into centre of cake comes out clean.
7. Leave in the tins for 5 minutes and then turn out onto a wire cooling rack. Carefully peel off greaseproof paper and allow cake to cool.
8. Spread jam over one half of the cake, and then sandwich the two halves together. Sprinkle the top of the cake with icing sugar.