Pre-heat oven to 190C (convention)/ 170C (fan-forced/convection). Grease and line a square brownie pan with baking paper.
Mix dark chocolate and coffee in a small saucepan. Place over a large saucepan halfway filled with water and melt chocolate on medium heat, stirring constantly until glossy and smooth. Cool.
Beat eggs, sugar and vanilla with an electric mixer until light and fluffy. Add cacao powder, hazelnut meal, salt and cooled chocolate. Beat briefly until well combined.
Peel avocados and remove the seeds. Place avocados and coconut milk in the jug of a blender and process until smooth.
Scoop chocolate batter and avocado mix in a large mixing bowl and mix with a wooden spoon until thoroughly combined.
Pour brownie batter into the prepared tin and bake in the pre-heated oven for 30-35 minutes until just done. Remove from the oven and allow to cool. Do not over bake or the brownie will dry out. Serve with a dusting of cacao powder.