• Preheat the oven to 180ºc / 350ºf / Gas 4.  Grease a 10 x 7 rectangle tin.
• In a bowl, mix together the margarine and caster sugar until light and fluffy.
• In a separate bowl, beat the eggs and add the vanilla extract.  In another bowl add the flour and baking powder.
• Sift a third of the flour in the butter mixture and combine, add the egg and stir together.  Alternate until all combined.  Pour into the tin and level.
• Bake in the oven for 25mins, or until golden (see tip).  Leave to cool.
• Turn out onto a wire rack.  Spread a layer of jam across the top and sprinkle with desiccated coconut and serve with custard.

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• If you press in the middle of the cake and it bounces back up it's baked.  If it leaves a finger print, put back in the oven until cooked.