Line a 12-section bun tray with paper cake cases. Put the butter, sugar and vanilla extract in a bowl and beat with a wooden spoon until light and creamy. Add the eggs and beat the mixture again, then sift in the flour and stir in. Divide the cake mixture between the paper cases.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 10–15 minutes or until risen and firm to the touch. Transfer to a wire rack to cool.
Knead together the red and the yellow icing to make orange icing. Roll a little piece of the green icing into a ball, then flatten into a round and gently push on to the top of a cake. Roll a larger piece of the orange icing into a ball. Place on top of the green 'pumpkin patch'. Roll a tiny piece of green icing into a stalk and push on to the top of the orange pumpkin. Use the black icing to make eyes and a crooked smile. Alternatively, draw the features on to the pumpkin head with a black icing pen.