First up preheat your oven to 180℃/160℃ fan/Gas mark 4. Grease and line a 30cm x 20cm baking tin.

Pop your margarine and sugar into a large bowl and cream together until light and fluffy. Add the eggs and Vanilla Extract and mix together until smooth and combined. Sieve the flour, Baking Powder and Cocoa Powder on top and then fold in until just combined. Pour in the melted Chocolate and milk and then briefly mix.

Pour your mixture into your prepared tray and smooth out to an even layer. Bake for 25-30 minutes until risen and a skewer inserted into the centre comes out clean. Leave to cool in the tin for 15 minutes and then transfer to a wire rack to cool completely.

Once your sponge it cooled, it is time to decorate; Break your Chocolate into pieces and pop into a bowl. Microwave in 30 second bursts stirring after each burst until melted. Leave to cool.

Pop your butter into a large bowl and beat with an electric hand whisk until smooth. Add your icing sugar in a couple of additions, mixing well after each addition. Pour in your Vanilla Extract and melted Chocolate and whisk together until your have a lovely smooth buttercream.

Spread your icing over your sponge using the back of a spoon or palette knife to create an even layer. 

Mix your Adventure Mix Sprinkles together in a bowl and then sprinkle over the top of your cake. Ta-dah your are now ready to slice up your creation and tuck in!