Heat the oven to 180C/160C fan/gas 4. Oil the base and sides of a 33 x 23cm cake tin (it should be at least 2.5cm deep) and line with baking parchment. Combine the flour, cocoa powder, baking powder, bicarbonate of soda, the sugar and a pinch of salt in a large bowl. Rub any lumps of sugar between your fingers to break them up, shaking the bowl a few times to bring them to the surface.

Whisk the oil, yogurt, vanilla and eggs together in a jug, then pour the wet ingredients into the dry. Stir well using a spatula or whisk until no pockets of flour remain. Pour the batter into the tin and bake for 30 mins until a skewer inserted into the middle comes out clean. If any wet batter clings to the skewer, bake for 5 mins more, then check again. Leave to cool in the tin for at least 20 mins, then turn out onto a wire rack and leave to cool completely.

To make the icing, beat the butter, sugar, 1 tbsp milk and the vanilla until soft and fluffy, adding the rest of the milk if it’s too stiff. Transfer 4-5 tbsp of the icing to a piping bag fitted with a 1cm round nozzle and pipe a border around the cake, leaving a 1cm gap between the edge and the border. Pipe on the halfway line, centre circle and penalty areas, then squeeze any remaining icing from the bag back into the bowl of icing. Dye the remaining icing green using a few drops of food colouring gel. Transfer the green icing to a piping bag fitted with a 1-2cm star nozzle, or grass/hair nozzle. Pipe small blobs of icing all over the cake, avoiding the pitch lines, until the sponge is completely covered. Decorate with mini figures and a chocolate football, if you like. Will keep in an airtight container at room temperature for up to four days.