Pre-heat the oven to 180/170℃ fan and line an 8 inch baking tin with parchment paper.
Mix the softened butter and sugar with an electric hand whisk (you can use a normal whisk or wooden spoon) and then add in the eggs.
Beat the mixture until thick and fluffy. Add in the melted chocolate and vanilla essence and mix in with the whisk.
Sift in the flour, sugar and baking powder and mix in with a spatula or wooden spoon until combined.
Pour half the mixture into the lined baking tin and top with the 12 snack size Twix bars. Then pour the remaining brownie mix into the pan.
Place into a pre-heated oven for 30 mins. Once baked, allow the brownies to cool in the tin and then chill in the fridge for 1 hour before cutting and serving.
