Combine the butter, sugar, salt, vanilla, milk, eggs, cocoa powder, and 1 cup of flour and mix well. Add the yeast mixture and stir to combine. Gradually add the remaining flour.
Shape the dough into a round and place it in a large greased bowl, turning once to coat. Cover with a plastic wrap and allow the dough to rise at room temperature until doubled, approximately 1-1/2 hours.