Preheat the oven to 180°C / 350°F / Gas mark 4.
Line an 8x8inch square baking tin with greaseproof paper. Set aside.
Place the dark chocolate and unsalted butter in a microwave-safe bowl. Melt in the microwave in 30-second blasts, mixing after each, until completely smooth. Set aside.
In a separate bowl, whisk the eggs and sugar for 1 minute until pale in colour and frothy.
Pour in melted chocolate and butter mixture, add the flour and fold the mixture together until fully combined.
Add the Maltesers and fold through.
Spoon into the baking tin and spread out into an even layer.
Bake for 17-20 minutes* until the top is no longer shiny and the edges have started to crack.
Leave to cool completely** for at least 4 hours or overnight for best results. You can speed this up by putting them in the fridge to set for an hour. This will give the brownies time to set and turn fudgy.
Slice into 12 and serve!