Preheat oven to 160 degrees celsius (fan-forced) and line a 20cm square tin with baking paper. Set aside.
Place the butter into a microwave-safe bowl. Heat for 1 minute.
Add the caster sugar and sifted cocoa powder and stir.
Heat in the microwave on 30 second bursts (50% power) until sugar dissolved and ingredients combined - stirring each time.
Allow to cool slightly.
Add the vanilla extract and the eggs and whisk until combined.
Sift the plain flour into the bowl and gently fold through.
Pour the brownie mixture into the prepared tin and bake for 25-30 minutes or until cooked through.
Leave in the tin to cool completely.
Thermomix Instructions - Click the link in the notes section below for the Thermomix recipe.