Place cubed bread in a 13x9 pan. In a large bowl, whisk together the milk, coffee, eggs, vanilla, sugar, cinnamon and cocoa powder. Pour over the cubed bread and stir until completely coated. Cover tightly with plastic wrap and refrigerate overnight.
In the morning remove french toast from refrigerator 30 minutes before baking and preheat oven to 350 degrees F. Remove plastic wrap and bake for 40-50 minutes, until golden and hot throughout.
In a small bowl, whisk together the powdered sugar and coffee. Drizzle over the hot french toast.