Put the margarine, oil, caster sugar, milk, cocoa, eggs and self-raising flour in a large mixing bowl.
Whisk, starting slowly and then speeding up until you have a light, smooth batter.
Line a 12-hole muffin tray with cupcake cases and spoon the batter evenly between them. I find the easiest way to do this is with a large ice cream scoop. Don't forget to level off.
Bake for 20-25 minutes until springy to the touch. If you take them out too soon, they'll sink.
Transfer the cakes to a wire cooling rack and allow to cool completely.
Make the walnut brains
Place the walnuts on a microwave-safe plate.
Mix the icing sugar, pink food colouring and 1/4 tsp water together to give a thick icing.
Paint the icing generously over the walnuts.
Zap in the microwave in blasts of 10 seconds until the icing has melted over the walnuts, giving them a pink glaze.
Allow them to cool before removing them from the plate as sugar can get very hot.
Fill the cakes
Use an apple corer to make holes in the cakes to about half way down. You can eat the offcuts!
Spoon or pipe the jam into the cores.
Place a walnut brain on top of each one and you're done!
If you like, you can use a tube of pink writing icing instead of making your own glaze for the walnuts, and then microwave them in the way directed.The cupcakes are best placed in a sealed container in a single layer. As they contain jam and nuts, I find they're best stored in the the refrigerator to keep them at their best for 3-5 days.