Image credit to: Boston Organics
1. Preheat oven to 375°F. Oil an 8-inch cake pan, then cut a circle of parchment and place it on the bottom. Oil that too.
2. In a medium bowl, combine the flour, cocoa, baking soda, salt, and sugar. Whisk together to break up any clumps in the cocoa. In a second medium bowl, combine the oil, coffee, and vanilla. Pour the wet ingredients into the dry and mix together until smooth. Stir in the cranberries or cranberry sauce. Add the vinegar and stir - you'll see light swirls of fizz form as the vinegar and baking soda react.
3. Immediately, pour the batter into the pan. Bake for 30 to 40 minutes, until a toothpick inserted in the middle comes out clean. If the cake is still liquid in the middle after 40 minutes, cover loosely with foil and bake for another 10-15 minutes, checking at 5 minute intervals.
4. Take the cake out of the oven and cool completely on a rack. When cool, frost with the chocolate icing.
5. To make icing: combine all ingredients in a microwave-safe bowl and heat at 20-second intervals until the chocolate is just melted. Stir until thickened and smooth but no more, otherwise you risk turning the icing grainy.