I preheat the oven to 350°F (175°C) and grease a 9×13-inch baking dish. In a large bowl, I whisk 1 cup flour, ½ cup cocoa powder, 1 tsp baking powder, ½ tsp baking soda, ½ tsp salt, and 1 tsp cinnamon. In another bowl, I whisk ½ cup melted butter, 1 cup sugar, 2 eggs, 1 tsp vanilla, ½ cup coffee, and ½ cup buttermilk until smooth. I combine the wet and dry ingredients, stirring until just mixed, then pour into the dish. I bake for 28–32 minutes until a toothpick comes out clean, then cool completely.