Preheat the oven to 180 °C. Heat the butter in medium pot until melted. Over low heat, stir in sugar until 80% dissolved, now add the chopped chocolate and allow to melt.
Remove from the heat and fold in the almond flour, cocoa powder, vanilla essence and eggs until well combined.
Spoon into a lined 20 cm springform tin.
Bake for 25 minutes, then switch oven off and leave inside for 30 minutes.
Allow to cool completely before serving.
For the ganache, gently heat the cream. chocolate and vanilla together until smooth and glossy. Pour over cooled cake. Top generously with berries and optional hazelnuts. Alternatively, replace ganache with crème fraiche or whipped cream.