Preheat the oven to 350°F (180°C) then generously butter a 10- to 12-cup Bundt pan, preferably non-stick. Add the coffee, butter, and cocoa in a large bowl and microwave for 2 minutes until the butter is melted. Whisk until smooth then set aside to let the mixture cool for 10 minutes.
While the chocolate mix is cooling, combine the sugar, baking powder, baking soda, salt, and flour in a large bowl. Pour the cooled chocolate mixture into the bowl with the dry ingredients, and mix until thoroughly combined.
In a large jug whisk together the vanilla, eggs, and sour cream. Mix into the chocolate batter, stirring until thoroughly combined. Pour the batter into the prepared bundt tin.
Bake the cake for 50-55 minutes, until a long toothpick or skewer inserted into the center comes out clean.
Remove the cake from the oven, wait 5 minutes, and turn the pan over onto a cooling rack. After 5 more minutes, lift the pan off the cake. Let the cake cool completely before glazing,
While the cake is cooling make the glaze: Combine the chocolate and cream in a microwave-safe bowl, or in a saucepan set over medium heat. Heat until the cream starts to bubble around the edges. Stir the warm cream and chocolate together until the mixture is smooth and shiny.
Once the bundt cake has cooked, transfer to a serving plate or cake stand and spoon the icing over the top of the cake, letting it drip down the sides. Cover and store the cake at room temperature for up to 3 days.