Mix all wet ingredients in a bowl and beat it smooth: melted butter + sugar + milk + vanilla

Now sieve all-purpose flour + cocoa powder + coffee powder + baking powder + pinch salt to the bowl. Mix it well without any lumps. Add chopped dark chocolate pieces as well

Now pour the batter to a baking vessel. Preheat for 10 minutes at 350F. Now bake it for 30-35 minutes

Refrigerate it for 2-3 hour before you cut it and serve