In a large saucepan, melt butter. Then add cocoa powder and stir until combine. Set aside to cool.
In separate bowl, whisk eggs and sugar together, keep whisking until dissolve.
Add butter, cassava flour, dry ingredients, and vanilla extract. Stir well.
Line baking pan with parchment paper. Pour batter in then top with chocolate chips and nuts.
Bake at 180 °C for 30 minutes