Preheat the oven to 180ºC, fan 160ºC, gas 4. Grease and line an 18cm round sandwich tin with baking parchment so that it comes 2cm above the top of the tin.
Put the baking spread, sugar and milk in a large bowl. Cream together using a hand-held electric whisk until light and fluffy. Gradually beat in the eggs, then fold in the flour and cocoa powder.
Pour the mixture into the prepared cake tin and bake for 30 minutes, until a skewer comes out clean. Leave to cool in the tin for 5 minutes, then turn out onto a wire rack to cool completely.
Meanwhile, in a small bowl, mix the icing sugar with 2 tablespoons water and the orange extract until you have a smooth, fairly thick icing. Stir in the red and yellow food colouring to create orange.
Spoon the icing onto the cake, spreading to the edges and letting it drip down the sides. Draw circles with the black icing, then drag a skewer from the centre to create a web effect. When the icing is set, decorate with a spider made from chocolate buttons and writing icing.
Cook's tip: if you don't have food colouring to hand, make chocolate icing by adding 1 tablespoon of cocoa to the mixture and use a white icing pen for the web.