Preheat your oven to 160°C/320°F (or 140°C/285°F for fan and convection ovens). Line an 8x8-inch tin with baking paper.
Melt the dark chocolate and the butter together over low heat on the stove then set aside to cool for around 5 minutes.
To a large bowl, add the sugar, eggs and vanilla extract. Use an electric whisk to mix it up until it becomes pale and frothy.
Add the melted chocolate mixture into the bowl with the sugar and eggs. Gently fold them together with a wooden spoon or spatula.
Stir in the flour and cocoa powder to make a glossy batter, then add the chocolate chips and your handfuls of Halloween candy.
Transfer the mixture to your lined tin and bake for around 25-30 minutes, until the brownie has risen and is pulling away from the tin slightly.
Let the brownie cool for around 20 minutes (or until it's warm to the touch, not hot) then gently press in your Halloween candy. The residual heat will melt the chocolate slightly and help it stick once cool.
Let your brownie cool to room temperature then transfer it to the fridge overnight to set.
Once set, remove from the tin, cut into squares and enjoy!