Follow the vanilla sponge mix instructions.
Preheat the oven to 200 °C, (170°C for a fan oven), or Gas Mark 6. Generously grease 2×7 inch cake tins and line with greaseproof paper.
Mix the cake mix, adding 2 eggs, 50g softened butter and 100ml water in a large bowl on low speed for 1 minute until moistened. Add the cocoa and red food gel to the mixture. Whisk at high speed for 2 minutes, until the mixture becomes thick and creamy.
Pour equally into the 2 cake tins.
Bake for 15-16 mins in centre of oven until it has risen and firm to the touch. Remove from oven and allow to cool.
Once cool, carefully cut a heart shape out of each cake.
Blitz leftover cut-offs of cake in a food processor to make the coating.
Make the buttercream for the filling and topping.
Sprinkle the blitzed cake on top.