1Preheat the oven to 180C/ 160C Fan/Gas 4. Grease and line the bases of 2 x 20cm deep sandwich tins.
2Sift the flour and baking powder into a large bowl. Add the rest of the sponge ingredients and beat until smooth and creamy. Divide the mixture evenly between the cake tins and bake for 25-30 mins until the tops spring back when lightly pressed. Turn the cakes out onto a wire rack; allow to cool completely.
3For the filling, break the chocolate into squares and put in a heatproof bowl. Stand the bowl over a pan of barely simmering water, making sure the base doesn’t touch the water. Leave until the chocolate is almost melted; remove the bowl from the pan and set aside to melt completely.
4Whisk the cornflour and yolks in another bowl until combined. Whisk in 1⁄2 the marmalade. Heat the milk in a small pan until almost boiling, then pour into the yolk mixture, in a thin stream, whisking all the time. Pour into the milk pan and cook over a low heat, whisking constantly, until it thickens into a custard.
5Immediately pour the custard onto the chocolate, then add the rest of the marmalade and black colouring and whisk to combine. Cover with clingfilm and set aside to cool completely.
6For the buttercream, beat the butter and icing sugar in a bowl until light and fluffy. Beat in the green food colouring, vanilla extract and 2tbsp cold water.
7Once the cakes have cooled, sandwich together with the black slime.
8Cover the top and sides with the green buttercream. Chill the cake for 30 mins.
9For the strawberry monsters, roll out 7 or 8 small discs of white icing. Cut a zigzag pattern across the centre of each one to give you 2 rows of ‘teeth’.
10Break 25g of the black ready-to-roll icing into 7 or 8 balls and roll out into small ovals on a surface dusted with icing sugar.
11Melt the white writing chocolate according to the pack instructions and use dots as glue to stick the teeth onto the black ovals.
12Stick these mouths onto the strawberries with dots of white writing chocolate and set aside to dry.
13For the tentacles, roll the rest of the black ready-to- roll icing into 7 or 8 logs, with one end thinner than the other. Curl each tentacle then dot a line down it in white writing icing. Stick 1⁄2 a cocktail stick into the thick end of each one, then set aside to dry.
14To decorate the cake, stir the icing sugar with 2-3tbsp hot water and the tube of black colouring gel, adding a few drops of water if needed to get the right consistency. Spoon on top of the cake, pushing it to run down the sides.
15Just before serving, top with the strawberries and stick in the tentacles.
