Preheat your oven to 160 degrees and line the base and sides of a 20cm square baking tin with baking paper.
Cut the Snickers in half lengthways and set aside.
In a large saucepan (you want it to be big enough to accommodate the extra ingredients added later), melt the butter, cocoa and sugar over a low heat – stirring continuously.
Add the vanilla essence and egg - whisking the mixture as you go.
Sift the flour over the mixture and whisk to combine.
Spoon half the mixture into the cake tin and carefully place the Snickers on top.
Add the remaining brownie mixture to cover the Snickers and pop into the oven and bake for 35 minutes.
Allow Brownie to cool in the tin before removing, cut into small pieces - or large pieces - there's not judgement here!