Line a 12-section muffin tray with paper muffin cases. Put the butter, sugar, marmalade, eggs, flour, baking powder and vanilla extract in a bowl and beat with a hand-held electric whisk for about a minute until light and creamy. Divide the cake mixture between the paper cases.
Cut thin strips from the candied orange peel and lay a couple of slices over each cupcake.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes or until risen and just firm to the touch. Transfer to a wire rack to cool.