Preheat the oven to 180 degrees celsius (fan-forced). Grease and line a 20 X 28cm rectangular baking tin with baking paper and set aside.
Place the dark chocolate into the Thermomix bowl and melt for 2-3 minutes, 50 degrees, Speed 2 (or until melted).
Add the avocado, banana, eggs and vanilla extract and mix on Speed 5, 10 seconds. Scrape down the sides of the bowl and repeat for a further 5 seconds.
Add the dry ingredients and the milk and mix on Speed 4, 5 seconds or until combined. Stir the raspberries through with the spatula.
Pour the mixture into the prepared tin and sprinkle with extra raspberries (if desired).
Bake in the oven for 25-30 minutes - when the brownies are cooked the top should be set and a knife should come out mostly clean when stuck into the middle. Remove the brownies from the oven and allow to cool for 10 minutes before placing in the fridge to cool completely.
Slice into pieces and store in an airtight container in the fridge for up to 3 days (or freeze for up to 3 months).