Preheat the oven to 180°C (160 fan) | 350°F | gas 4 and line a 12-hole muffin tin with paper cases.
Beat the egg in a jug with the oil, milk and marmalade until well mixed.
Mix the flour, baking powder and sugar in a bowl, then pour in the egg mixture and stir just enough to combine.
Divide the mixture between the paper cases and bake in the oven for 20 - 25 minutes. Test with a wooden toothpick, if it comes out clean, the cakes are done. Transfer the cakes to a wire rack and leave to cool completely.