Preheat oven to 180C/350F and spray a 9 or 10 inch pizza tray or other flat bottomed round dish.
Place butter and chocolate pieces into a heat proof bowl and place in the microwave in 20 second increments, stirring in between each one, until all the butter and chocolate is melted and smooth. Leave to one side.
Place sugar, eggs and vanilla extract into a large bowl and whisk until well combined and the mixture is a little frothy.
Place the salt, baking powder, flour and cocoa powder into a small bowl and mix briefly to combine.
Pour the slightly cooled melted chocolate into the sugar and egg mixture and whisk until well combined.
Tip in the flour mixture and fold gently until there are no lumps of flour and everything is combined. Don’t go mad and beat the mixture though.
Tip the brownie batter into your prepared dish and smooth into a level layer with the back of a spoon/spatula.
Place in the oven for 22-28 minutes, until slightly risen, the top looks matte and only a few crumbs come out when you stick a skewer into the centre. You want the brownie to be ever so slightly under done, if you wait until the skewer comes out completely clean, the brownie will be overdone and tough when cooled.
Leave to cool completely before removing from baking dish/tray and placing on a plate. To make frosting: Place the butter, icing sugar, vanilla and salt into a large bowl and start to mix with a hand mixer on low. Once the icing sugar starts to combine, turn the speed up and mix until you can’t see any icing sugar, (mixture probably won’t be light and fluffy at this stage) then add the milk 1tbsp at a time, mixing in between each addition until you have a thick and creamy frosting.
Add in orange food colouring a little at a time and mix in between additions until you have desired colour. I used a Wilton gel colour and needed very little colour.
Spoon the frosting into the centre of the brownie pizza and then use a small angled spatula to spread and smooth the frosting over the top of the brownie.
To decorate: randomly place Halloween sweets and chopped up chocolate bars all over the top.
Slice into wedges and enjoy!
Halloween Brownie Pizza will keep covered, at room temperature for 3 days, or in the fridge for 5 days.