Preheat your oven to 160 degrees and line the base and sides of a 20cm square baking tin with baking paper – this will help you to remove the brownies once they are cooked.
Place the butter, sugar and cocoa into your Thermomix bowl and cook for 3 minutes, 60 degrees, speed 2.
Add the peppermint extract, vanilla extract, eggs and flour and mix for 10 seconds, speed 5.
Scrape down the sides of the Thermomix bowl and mix for a further 5 seconds, speed 5.
Pour the brownie mixture into the prepared tin and smooth the surface. Place the brownies into the oven to bake for 35 minutes.
Remove brownies from the oven and allow them to cool completely in the tin.