Preheat the oven to 350°F (180°C). Generously butter a 10- to 12-cup Bundt pan, preferably nonstick.

In a large microwave-safe bowl, combine the coffee, butter and cocoa powder. Microwave for 2 minutes, or until the butter is melted. Whisk until smooth, then set aside to cool for 10 minutes.

While the chocolate mixture is cooling, combine the sugar, baking powder, baking soda, salt (if using) and flour in a large bowl. Pour the cooled chocolate mixture into the dry ingredients and stir until thoroughly combined.

In a separate bowl or jug, whisk together the vanilla, eggs and sour cream. Add to the chocolate batter and stir until smooth.

Pour the batter into the prepared Bundt pan and bake for 50–55 minutes, or until a toothpick inserted into the center comes out clean.

Remove the cake from the oven and let it rest for 5 minutes. Turn the cake onto a cooling rack, wait 5 more minutes, then lift the pan off. Let the cake cool completely before adding the glaze.

To make the glaze:
Combine the chopped chocolate and cream in a microwave-safe bowl or small saucepan. Heat until the cream begins to bubble around the edges. Stir until the mixture is smooth and glossy.

Once the cake has cooled, transfer it to a serving plate or cake stand. Spoon the glaze over the top, letting it drip down the sides. Cover and store at room temperature for up to 3 days.